Piston selection should be made after you know what the cc's are of your combustion chamber. This is best done after the heads have been assembled as milling the heads can change the cc's, the valve type and/or valve job can change the cc's, and cc's can also be changed should you have any chamber work.
If you are not at a high elevation, ie Denver, you want to shoot for around 9.0 with iron heads so you can run pump gas. You can probably go a tad bit higher based on cam selection and "quench," but it seems no higher than 9.5 compression. Quench article here: What Is The Ideal Quench Height? - Hot Rod Network
You would want to try to achieve around a .045" quench - the distance from the top of the piston to the flat surface found on the head that surrounds the chamber. This forces the air/fuel mixture into the chamber and can eliminate detonation.
The typical Pontiac piston top is about .015" - .020" down in the cylinder bore and trying to get a good quench area can be done a number of ways. Some will mill the block surface to achieve a "zero deck" clearance where the piston top is even with the piston. There is plenty of material at the top of the block to do this, but you might change other geometry angles, ie the head's intake surface, which may need to be milled a matching amount. The valley pan may need some trimming to fit/seat squarely. You also want to ensure that none of your head bolts bottom out and crack the block - so depending on head gasket thickness used, they should be checked/mic'd. I have used the ARP head studs and mistakenly ordered the RA IV studs which have a couple longer studs than the standard 400 head and inserted an extra washer under the head to get the length correct - might not be the correct or advised way to do things, but it worked with no issues.
Another way is to have your machinist measure the distance from the crank's rod throw to the top of the block's deck surface and calculate where the piston pin needs to be located, using your connecting rod of choice, to get the top of the piston even with the block's deck. This is something done if ordering a set of custom pistons-to-order.
Both of the above methods make it easier when ordering head gaskets as having a "zero deck", you simply order a head gasket having a .045" crush. (Some will say .040" works as well, but I use .045" based on what my machinist recommends to take into consideration the heat of expansion, future wear, and even stretch at higher RPM's. If you use nitrous on the engine, he recommends more and says some of his nitrous engines go .060" or more if a really big shot.)
The third option, which I went with on my 455 I am building was to use a thinner head gasket along with the pistons being down in the cylinder .020". I purchased a set of Cometic brand head gaskets ( which run about $100 each, but are some of the best) having a thickness of .027" So, the .020 "down in the hole" plus the .027 gasket equals a quench distance of .047" which is right about where I want it. I also plan on about a 100-125 HP shot of nitrous.
So why is this important? The cc's of your head, the cc's of the area above the piston to the block deck, and the cc's of the head gasket you select will all add up to a total number of cc's. With this information in hand, you can then use one of the online compression calculators to determine
how many cc's you will need to incorporate through either a dished piston or the valve notches found in the piston tops to achieve your 9.0 +/- compression ratio.
Additionally, depending on cam lift/duration and cam advance/retard, you want to make sure the valve notches in the piston tops will give you the needed clearances so the valves don't kiss the piston tops.
Cam selection is one of many opinions and I have mine. These are by no means absolutes. The cams with the 110-112 Lobe Separation Angle (LSA) work better in a street engine with less than 9.0 compressions as they build additional cylinder pressure. The cams with 113-115 LSA (like stock cams) work better in a street engine with over 9.5 compression as they can lower cylinder pressure at lower RPM's which get picked back up at the higher RPM's. So for me, the compromise for a street engine having 9.0-9.5 compression is 112 LSA. This is what I selected for my 455 build.
Other important factors are Intake Closing point, duration, lift, and valve overlap. For lift, stock heads don't flow much past .450" lift and is why Pontiac cams increase duration versus lift, EXCEPT for the better breathing RA/SD Heads.
So, would the "068" cam work with lower compression- yes. Might there be a better choice - probably. LOL You don't want to go much over 280 degrees duration for the street, and less can sometimes be even better depending on trans/torque converter stall & rear end gearing. Build a Pontiac for Torque over HP. Perhaps the "068" ground on a 112 LSA might be a good cam with 9.0 compression.
I did a comparison, perhaps not 100% accurate by any means, but still a good comparison, using the 1977 Trans-Am Cam specs in both the 400 & 455 engine. This cam is not what I would consider very radical, but a good street cam. I used an engine Dyno program giving each engine a streetable 9.25 compression. Then I changed the rate of valve lift which mirrors the assorted Pontiac factory cams while still using the 1977 cam duration and LSA. Each engine can be compared at a base line of 2,000 RPM's and then for a maximum HP & TQ at their best RPM. You will see that the HP increases quite a bit from the base line to the maximum/best HP number, but the TQ not so much because the torque remains strong and somewhat flat throughout the entire range - which is what you want as TQ is what moves the car and smokes the tires. The .469" of lift would be about max for stock heads. See attachment.
Roller cams certainly have their advantages, probably more over a flat tappet cam. The down side is of course cost. I am also one who would strongly recommend using the lifter valley brace when using a roller cam - and I would not do without it if I used a roller. As far as bad cams, I think there are many factors that go into those stories & experiences of them going flat. I read that many issues stemmed from the Chinese lifters that were being introduced into the country in high numbers and cheap cost - they were junk. That has since change. How bad can a flat tappet cam/lifters be when you have a supplier who sells both roller and flat tappet cams guarantee them not to go bad or they will replace them? Our cams are guaranteed not to go flat!
First is improper break-in, from not using a good cam/lifter lube that sticks to the parts rather than a slimy liquid that runs off. (I would venture to guess that some people have put the lighter cam lubes on and then let the engine sit for a while. By the time they were ready to fire up the engine, the lube had all but dripped/seeped off.) Installing the cam/lifters and a good break-in lube should be done when you are just about ready to fire up the engine - its in the car and you are buttoning it all up.
Using improper break-in oil. A good specific break-in oil with the correct amount of Zinc in it should be used. You can also add a Zinc additive to other oils that may not have the needed amount, but I think the best way to go would be to use the correct formulated oil right from the start. Using an oil that is too thick - which can affect the flow/bleed rate of the lifters which can mean not enough oil supply at the most critical time in breaking in the cam/lifters. I plan on using the Brad Penn break-in oil, but the Joe Gibbs break-in oil also gets good reviews. I will then follow up with the oil with the formulated Zinc additive before going to the store bought oil and adding a container of Zinc additive like Rislone puts out.
Priming the engine just before starting. Again, don't prime the engine and let it sit for a week or more. It would also be a good thing to rotate the engine by hand to ensure all air pockets are worked out and oil gets to all places it needs to go. My machinist uses an oiling pressure system that he taps into the oil pressure fitting and pressurizes the oil into the engine.
Several lifter suppliers now offer their lifters with a small hole lasered into the base that lets a small amount of oil to seep out onto the cam lobe thus lubricating the cam/lifter. Rhodes Lifters have a tiny channel that runs along the side to do this, and there is even a tool that will scour the lifter bore and allow oil to flow down the channel much like the tiny channel found on the outside of the Rhodes lifter bodies. I would go with the Rhodes before scouring my lifter bore with a channel.
Many install BIG lift cams that require heavy pressure valve springs - typically a dual spring set-up. The added pressures, along with many who then add the higher 1.65 lift rocker arms, puts excessive pressures on the cam lobes/lifter bases and can cause them to wear prematurely if there is any starvation of break-in lube or oil. It is suggested to run just the outside spring for cam break-in and then add the inner spring once this is accomplished. It is the spring rates that really determine this. I am using double valve springs and my machinist said I don't have to pull the inner springs to break in my cam. I think my lift is .490" on the cam I am using.
Varying the engine speeds when breaking in a cam is important. Have seen a few YouTube videos claiming first time fire up and they let the engine idle or rev the crap out of it. My machinist uses an engine break-in stand and says he likes to vary the engine speed and get the engine up to temperature and then shut it down to allow it to cool. He repeats this a couple times. It works for him and he would not be doing it if it caused problems.
You also want to have the timing adjusted as soon as you get it fired. I have never experienced a cam failure, but that was when oil had all the ingredients to protect them from wear.
So roller or flat tappet is a choice and I'd go with whatever you feel most confident with. For me, its about cost and the roller set-up is more than I care to spend for a street engine. If I were to go all out with aluminum heads, BIG HP & TQ, then I'd step up to the plate and go roller.
For rods, you have choices here too. I like light rods - less rotating mass. I think the forged I-beam rods might be lighter than the H-beam's. They are just like stock rods except forged. The H-beams are for higher HP engines and strokers. For a street engine and cost effectiveness, I'd go with the forged I-beam rods.
Piston choice, once you know how many CC's you need out of them, can be almost any manufacturer. Forged are the best, but most expensive. I went with the ICON FHR pistons on my 455 build as they were forged and meet my goal of 9.0 compression. Hypereutectic piston can be a reasonable cost. I used these in my brother's built up Mopar 360CI street engine. These are better than cast, but not as good as forged - kinda in between in my opinion. Some love them, other hate them. Lastly are cast pistons. Fine for a stock rebuild and will hold up if kept under 6,000 RPM's.
With new pistons/rods, you will have to have the engine balanced.