I wouldn't buy a kit. I'd buy individual parts. You don't know what your overbore will be, or your bearing undersizes. The best cast pistons are probably the SP 357P. The cheapest forged pistons are from Auto/Tec, for around $500 shipped.
If your overbore is .030 here are some pistons & moly rings.
http://www.ebay.com/itm/Sealed-Powe...ash=item2364e3a18b:g:cioAAOSwv9hW5~rn&vxp=mtr
https://www.summitracing.com/parts/slp-357p30/overview/make/pontiac
https://www.summitracing.com/parts/pcr-40076cp-030/overview/
https://www.summitracing.com/parts/slp-e-245k30/overview/
And there are much better cams. That one is a single pattern, with a 110 LSA. On a fresh rebuild, the small 256 Voodoo that was mentioned earlier, might be a good choice. OR, to save a few bucks, you could go with the Summit K2800 cam & lifter kit.
http://www.lunatipower.com/Product.aspx?id=1774
http://www.jegs.com/i/Crower/258/66...3Q0XZ8a7NUNyFhaD_U4xHOs7i-NITnmmWbRoCJ_jw_wcB
https://www.summitracing.com/parts/sum-k2800
The Melling M45DS oil pump is sorta std equipment for most street Pontiac engine builds. That's what I used in all my Pontiac engine builds.
https://www.amazon.com/Melling-M54DS-Replacement-Oil-Pump/dp/B000C4PO6E
I don't think there are any 350 Pontiac head gaskets made now except for the high priced brand. Most guys just use the Fe-Pro gaskets which were made for 400 & 455 engines. The bore size is 4.3", which is much larger than the 350 bore size. This will reduce compression. You can go with thinner Cometic gaskets, to increase compression. If your deck height is zero, you can go with .040 thickness. If it's .005 you can go with .036 thickness, if .010 go with the .030 thickness, & if over .010, go with .027 thickness. This will help keep the quench distance close to the recommended .040 number. These gaskets can be made for blocks with or without the chamfers at the top of the cylinders. It is said that the deck needs to be a certain smoothness, for these gaskets to seal correctly. So, you need to make sure your machine shop can produce this type deck surface.
http://www.jegs.com/i/Cometic-Gaskets/245/C5710-040/10002/-1
http://www.jegs.com/i/Cometic-Gaskets/245/C5710-036/10002/-1
http://www.jegs.com/i/Cometic-Gaskets/245/C5710-030/10002/-1
http://www.jegs.com/i/Cometic-Gaskets/245/C5710-027/10002/-1
If you plan to use a Voodoo or similar cam, I'd have screw-in studs installed in the heads. If your budget can stand it, I'd also go with new stainless valves. There are 2 ways to do the screw-in studs. I think the most popular way is to use the ARP studs which have a 7/16 top, but 1/2" base threads. With these, you simply pull the old studs and tap the holes for the new studs. If the holes are not deep enuff, some will have to be ground off the bottom of the ARP studs, since the base thread portion is longer than stock studs. The other way is to pull the studs and have 7/16 heli-coils installed. Then you can use the BBC type studs, which have 7/16 base threads. BUT, since it will probably cost $200 or more to do the screw-in stud thing, I'd recommend buying some good 6x-4 or 5c-4, or the late '73 & '74
#46 heads. All these heads have screw-in studs and factory hardened valve seats.
http://www.jegs.com/i/ARP/070/290-7201/10002/-1
https://www.amazon.com/ARP-290-7201-Rocker-Arm-Stud/dp/B001T6CRDC
http://butlerperformance.com/i-24452864-arp-7-16-x-1-2-rocker-stud-kit-arp-290-7201.html
"...anyone have a thought on how much an engine shop would charge to tear down and build up the motor using parts I'd supply? Rough estimate?..."
That price can vary WIDELY. Some prices are reasonable--MANY are not. AND, here is the best advice: don't have it built by a shop that has very little experience building Pontiac engines. A Chevy shop can REALLY mess up a good Pontiac engine.
But, if I had to make an estimate, I'd place it at $1000-$1500 just for machine work & labor.