Hello All. New to this forum. Hopefully someone can help me with my 402 rebuild. I am restoring my 1970 GMC sierra grande truck. I am currently going thru the engine. The indication is that is came with a 396 but i understand they marked the 402 as 396 also during this time. I have the engine apart and have done some research and found this is a true 402 block 0.040 over bore to 4.166. I want to get about 400+ hp when done. i think I can stay with my block/heads/crank. I want a good street rod and occasional play at the track but mainly street. Here is what i think I know.

Block:
Engine ID - T0406TBG
Casting - 3969854
2 bolt
This seems to be a 402 block built at the Tonawanda plant April 6th 1970 for a truck. Could pass as original equipment I believe but has been rebuilt at some time.

Heads:
Casting - 3931063
Open chamber
2.06/1.72 valves
From my research I have seen some info that indicates 96.4cc and some 100.9cc. Not sure which is correct.

Crank:
Casting - 3904816
Rod journals at least have been undersized 0.010. Going to mike out this weekend to verify these and mains.

Pistons:
Currently marked with "402P" on one side and "F" on the other. I think they might be sealed power cast pistons but data says a 0.125 dome but I measure 0.10 dome. doesn't look like they have been milled down because the 0.040 markings still have raised edges. Doesn't seem to have a lot of wear but again they will be miked this weekend along with the bore. The rods are stock.

I have done the math and believe with this setup my piston deck is 9.750 which would put the dome deck to 9.850. I am thinking about just going with having it bored to 0.060 anyway which means I would replace the pistons. From what I have read the stock crank/heads/rods are plenty strong for my use.

My main trouble is the geometry between the pistons/cam/push rods/rocker ratio/valve springs etc. I can't find any formula to determine this and I don't have the experience to just know. Do I want to go roller cam? What duration/lift? I have found plenty of info to check these clearances once built but nothing to check before parts are purchased.

Thanks for any help to get me started.