360 build

While more compression does help,it has to be matched to the ports ability to breath,the chamber design,fuel being used,cam being used etc.More compression will give an increase of tq and h.p across the entire power band but the rest of the components must match.You could make well over 600 h.p with twin turbo's and 8:1 compression. But you can also make 600 h.p by virtue of big cid and lots of compression

For example it does no good to install an rv grind cam in a 16:1 race hemi.The rv cam doesnt help in an 8:1 turbo engine either.
But the rv cam works nicely in an 8 or 9 to 1 motor that needs lots of torque down low. A mismatch will result in a poorly performing engine that is sluggish.No amount of tuning will help it.Lets say you decided to ignore my advise and go with 7.5 or 8:1 and a biggish .480 lift cam. While the engine will run and probably drive O.K,it will have weak low end tq. And you will be leaving h.p and tq on the table across the entire rpm range.More compression does come with a price. Pinging due to crap fuel or too much timing advance can be hard on an engine. Be sure to polish everything in the combustion chamber to prevent hotspots

I'd say you will be looking at closer to 400 h.p with 9.5 compression and a well matched cam.

You can still use the pistons you have. Just have the block cut to square everything and shave the heads to reduce the chamber volume. You will also need to have the intake side of the heads shaved to match and have a good seal.

For your engine go no higher than .480 lift. You need to look around and do some reading,learn some about cams,compression,heads etc. Do you have any books?