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I believe the M20 will be fine. I think lots of times folks get hung up on ratings. Same happened with my TH350 I had behind a 400 small block in my 69 Camaro back 30 years ago. I had that motor really built and threw a 140 shot of nitrous on top of that. Ran 11's and I beat the snot out of it every weekend on the street. The only thing I ever broke in the driveline was a rebuilt 8.2 GM posi after almost 4 years of this abuse. Now, that's anecdotal evidence and I may grenade this M20. However, after returning the old one to the guy who built the replacement, I'm only out $850. So, if that $850 turns out to be money spent poorly, I'll get on AutoGear's waiting list for a wide ratio M22 and pony up the $2300 they want... I guess time will tell... 馃嵒
I asked Darrin from Nitemare about how long a stock built Muncie (M20) would survive behind the 461 I have in my car now. His take was that it would be fine for a street application. Same with the factory 10 bolt. I've put ~1200 miles since the engine went in the car and the rear and transmission both seem fine. That being said, things could change if I decided to throw some super sticky tires on the back and bring it to the track.
 

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I was thinking that about showing it in the car too @Jared . I just didn't want to do it too soon as I'm still a few weeks out from my swap. I would be happy to show it to you though...

On the M20 and 10 bolt, I agree completely. Mine is not an over the top built motor and I'm not dumping the clutch with drag radials on. When I talked to Mike at Ram clutch, he said that so many guys go strictly by HP ratings and estimates. He said, while that might be safe, it's often completely unnecessary and guys end up with a leg shaker of a clutch because they over bought. He said long before something breaks or the clutch slips, the tires will break loose.
Keep me posted if you don't find someone before it's ready to come out. I'd be looking at this as a potential backup for the future so I'm kind of a bottom feeder on this one. That being said, for the right price I'd help you pull it.
 

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One way to tell is the large number cast near the distributer. Some year blocks had the year cast in fairly large numbers on the drivers side under the distributer. The numbers are large and face the back of the block. Engine in mine now is from a 1971 and has a large 71 and the one that came out was from 1974, large 74 cast in the same spot. I'm not an expert and am not not sure if this carries to the older engines. Either way, if it's there, you should be able to see it.

Here are a couple more resources to narrow down what you have.


 

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You guys are making me want to keep it! LOL....
If you have the space, it may not be a bad idea. A buildable core is pretty hard to find. Yours being a runner is an added bonus. If you go this route, be sure to prep it for storage so it's still good should you need it. A little oil in each plug hole, make sure it's completely drained out, and then tape up any openings to keep rodents out. Easy enough to replace gaskets when/if you need it.
 

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It's a fine plan but I'd really like to recover the money @Jared. I may kick myself one day but right now the mission creep that's already happened in 2 months of ownership is just unreal....

Plus tonight Christine did no behave herself. I noticed a while back that she only had 2 bolts in the door hinges on the door side. One upper and one lower. Both driver and passenger side were the same. Today a set of hinge bolts came in the mail so I figured hey, it's 85 in the garage with 85% humidity and I've already showered and put on nice clothes for the day but... how hard can it be to add a 4 bolts to each door right? Needless to say, my clothes are in the laundry and I just got out of shower two... and I only added 4 of the 8 missing bolts... and scratched the driver side door with some miss adjustment on try number 397.... So, she is on the naughty list tonight.
Better get used to this sort of thing. I've owned mine for 10 years now and it's spent way more time on stands than actually moving under it's own power. To add to the equation, Pontiacs are expensive to build and parts availability can be a bit frustrating. I ran into your mission creep when I did my engine a couple years ago. Started with a short block, priced out heads, and set what I thought was a very reasonable estimate for cost. Then the "while I'm in there" and "I didn't realize I'd need this" set in and I went a few thousand $ over budget. By the time I was done, the only parts I reused from the old engine was the bell housing, alternator, power steering pump, fan, brackets, and the pulleys.

Free advice on your car would be to give it a very fine tooth comb look over to see what else the PO didn't put together properly. Missing hinge hardware is a concern and not just for what you found. I would be wondering what else they didn't reassemble properly.
 

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I'm thinking Baaad's sale price is a good indicator on what you can expect to ask and possibly get. Maybe Pontiac blocks/engines/buildable cores are plentiful elsewhere, but they are scarce in New England. When mine grenaded a couple years ago I didn't think the engine coming out was rebuildable (after disassembly I think it may be so it's sitting wrapped in a corner now). I started out looking for a good core locally. The only engines that came up over the course of a 2 month search were two that looked like they had sat outside for 30 years and were priced close to $2000. I'd try to sell it running in the car and ask around $3k or so. If you think you're a month out, try selling it now and negotiate that it stays in the car until you have the other engine ready to go in.
 

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Not much of a fan of the looks of GMC or Chevy trucks since the square body. Oh, the wife drives a Grand Cherokee so we have all 3 brands covered... 馃槵
Only three name plates covered? You've got some work to do. Between the wife, my kids, storing a car for my dad, and my fleet of junk we have 6 different makes of cars at the house with each decade between now and the 1970s represented. Chevy wins with the most at 3.
 

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Sweet! I actually forgot about the trailer so make that 7 different makes. We have a strange mix here. My oldest is an import car guy. Some are turned off by this but he has a lot of wrench time on some of his cars.

1970 LeMans Sport
1981 Corvette (dad's)
1994 Mustang GT (running crappy right now, needs work)
2002 Miata (oldest son)
2008 Cobalt (younger son)
2018 Hyundai Elantra GT Sport (oldest son)
2019 Honda Fit (wife)
2020 Colorado RST
Big Tex car hauler

My garage only holds 2 cars so my driveway looks like I'm running a used car lot.

We have fallen far away from valuing @System 's engine for him.
 

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Well boys, the time has come. The 400 is out of the car and my buyer lands at the shop doing the swap tomorrow. It ran so well on the trip to the shop that I briefly wondered about my intentions... Anyways, next week the real work starts with all the new parts going in. Fresh 428 and M20, Yukon LS diff and DANA 3.55's with aluminum cover, new master and brake booster conversion from manual brakes, Dougs headers, Pypes H Bomb exhaust with turbos, Granatelli cutouts, Borgeson steering box and rag joint, CVF serpentine conversion, DEI HEI and wires, Quick Fuel 4150 carb, Carter fuel pump, Tuff stuff starter, Ram clutch and flywheel, Flowkooler water pump, etc....

Yeah, there was mission creep with my simple engine swap... When she gets back home, I'll do my Dakota Digital gauge swap and install my audio equipment. Then throw a cover over til spring and try to recover financially... Or order more parts to install next spring... I wonder which way that will go....
Nice list of upgrades! Which Ram clutch are you going with? I had a 10" Ram clutch behind the 400 that came out of mine. I went with the 11" McLeod for the new engine.
 
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