Port sizes, valve size, and combustion cc
The 360 heads will flow better because of the larger ports and valves. And you can port them to flow even better. With your piston choice compression isn't going to be an issue so for me 360. Heads are a no brainer. Flow makes hp. The engine has to breathe and 360 heads are gonna give you a advantage. The 302 318 heads only have an advantage if your trying to build compression which you don't have to worry about that.
9.5 is a good scr!
You will be around that with stock 360 heads with those pistons (kb399)
If you want more you can always work the heads and or get a thinner head gasket.
