OK, I see the problem I am facing, it was so basic it flew right over my head. I am trying to squeeze a smaller volume 38.125 cubic inch cylinder of a 305 into the same large 64 cc space (combustion chamber) as the stock 340 42.5 cubic inch cylinder. Naturally, since I start out with a smaller volume, I am not squeezing it down as much, hence the compression works out to about 8.5 to 1 rather than the factory 10.5 to 1.

Now I see in place of the factory flat top piston with valve reliefs, which displaces a negative value of -5cc or -7.5cc, what I will need is a piston with a dome displacement of around 10cc to make up the difference. The only problem with that (in my own mind anyway) is I can only picture the piston smacking the combustion chamber OR, worse yet, the valves smacking the pistons on the way up. The only other alternative I can think of (which is impossible, of course) is a 49cc combustion chamber volume.

I suppose what I really need to see/find is a Mopar 305 Trans AM piston so I know what I am dealing with. I wonder who made/makes those? Maybe what I need is a 340 12.5 to 1 piston, which in my 305 might figure out to be 10.5 to 1 piston?