need to raise compression w/o new pistons

The amount to mill for a specific CR increase depends on the head. Larry Sheppard's, How to Hot Rod the Small Block Mopar, gives the amount to mill for the specific combustion chamber size. I'm running the Mopar .024 - .028 compressed head gaskets and have had no problems, so that's a cheap way to increase CR. The only way to really know what cc your combustion chambers have is to cc at least one chamber per head and then do the math required to figure out the correct amount to mill. I say this because cc size varied even on the same casting heads and someone may have milled the heads in the past. Also, as mentioned above, you must check how much your piston is down in the hole at TDC. Once you have all this info you can go to the Keith Black Piston website and use their compression calculator to give you the true static compression ratio. As an example, after I got all the info I used their calculator and came up with an 8.66-1 C/R for my 318. I used a short duration/high lift cam (267/485) and have a very responsive little 318. Keep the camshaft duration in-line with the final actual compression ratio and it should be a good running engine, even with 8.5 - 9.1 compression. Let us know how it all works out.