Budget 318 build

Ok so im looking at some of these pistons on summit if i where gonna go to the 360 heads could i use a kb flat top to gain some of my compression back without any machine work? I looked up some pricing and thats just out of reach right now i found a set of kb flat top for 136 that may be doable how much compression gain will it give me? The 360 heads is an option i already have the heads laying around so it wouldn't cost nothing to bolt them on I have alot of work to do to this car to get it driveale I dont really want to spend alot of money on an engine that already runs if you know what I mean I am currently rebuilding the front end ball joints bushings tierods steering gear tires etc the i have to do body and paint and interior. There is two differen compressio heights on these pistons what does that number mean?