Did you ACTUALLY measure your compression ratio? Did you do a .500 down fill, cc the heads and do the math? If not, you don't know what your CR is.
I hate to be the prick, but just because the piston comes out of the bore doesn't mean it's a pop up. By no stretch of th imagination they ALL had FLAT TOP Pistons. There ain't a swinging Richard in the piston industry that calls a FLAT TOP piston a pop up. No F'ing way. I'm anal about this because this is just another reason how and why guys get jacked up with things. We all need to use the same vernacular or we might as well be speaking different languages. FLAT TOP PISTON was OE in EVERY 340. I've never seen a factory 340 out of the hole that I can remember. In fact, the prick engine builder I used in high school would NOT deck my block on my first rebuild to get the piston out of the hole. That prick is why I became an engine builder. They ain't all chevies.