Try a Silvo-Lite 3468 HC Hypereutectic piston. It should work well with Propane. It has a small recess in the top of the piston which will allow for a slightly higher than standard cam lift. Increased compression is really only needed if you're running a radical cam that needs to squeeze what's left of the cylinder volume tighter after keeping the intake valve open partway up the compression stroke. The hotter the cam, the higher the static compression ratio needs to be just to get cylinder pressure back up to where it used to be with a short duration cam.
Jerry
