Budget 318 build

You can raise compression with piston by either bigger bore, or pistons that go up the sleeve higher. Your factory pistons are already flat tops. Another thing is, if you put your money in the heads, they will work great on your future 360 and save you a ton. If you are not worried about every single hp from your 318, I'd stick with stock pistons and do a good job on your heads. mild porting (home works well, I've done videos for how-to), good valves/valve job and guides. Cut them .040 and they will work awesome on your 318, and will be 360 ready. My 2 cents