How much will 70cc heads raise my compression? Also how much lift?

Measure what? As I said pistons are .100 down the hole, which from what I've read is about average for the 400. I'm just trying to get an idea how much would 20cc less of combustion chamber volume would raise my compression? A ratio? 2? 3? 20? Lol.. I guess anything would be better than the crappy 7.8:1 or so they actually had from factory. I'd be happy with 9.5 or more, which thats around what my guess would be but I'm no expert and have no idea what the dimensions are of the stock pistons as far as dome volume, etc to plug into a compression calculator, Google hasn't answered the question much either. I know there's guys out there that's put closed chamber heads onto these low compression boat anchors before.

Also when loozing for a camshaft selection, from what I've heard it's easy to over cam a low deck, like you don't want to go much over a .235 duration, but is that still the case with high flowing cylinder heads? Also what's the most lift you can get away with, not having valve reliefs in the pistons? I've read in some forums of guys using cams like the .528 purple shaft with 1.6 rockers which comes out to .560 on stock piston 440s and 400s before but Idk if I want to risk going that high... it would be nice to though, I would just like to have an idea before I purchase a cam, lifters, springs, pushrods to match, and find out the cam won't work, and then stuck with a cam I can't use or return being it has been installed.
Thanks for your patience and forgive my ignorance, my experience with the particular engine, and combo is limited.