318 compression ratio

You can't zero deck heads. The piston can come up to the top of the block and that would be called a zero deck piston. Milling the heads is a way to increase the compression ratio and it is a math equasion dealing with the amount of cc's in the head.

MoPar has a "Engines" book that tells how to do this and how many cc's for the head to mill for a point raise in ratio. Which would probably be just great so long as it's actual ratio is 9.5-1 and not just working off the advertised ratio which is high for what it is actuallly.