340 build

Using a dial indicator is best, but however you do it, get a piston at TDC and measure its height above deck as precisely as you can.

BTW, those are TRW forged pistons. Nice. They would normally have the same compression height as the stock cast early 340 pistons, which is .018" above the deck. But measuring it is a good idea to see where, in case the block has been decked. Pulling them would be good, to look for cracks, broken rings, etc. I personally would put in fresh set of rings with the hone. Being forged pistons, the piston to cylinder clearance will probably (and should) be up around .003" to .004", typically.

Are the heads perfectly flat outside of the main combustion chamber? Or is there a very shallow circular machined area around the main combustion chambers that is about the size of the head gasket hole? (I just can't see for sure in the pix.) That fact is important to know for CR; there are 63 and 65 cc chamber Edelbrock Performer heads.) The ones with the shallow machined areas around the main chambers are intended for 340 pistons like yours.

For targeting static and dynamic CR, what is the intended use? That will drive the cam and will in turn drive the CR targets.

I have never seen a cam lobe like that.... wowzer!