Technical Milling 1955 Caddy 331 heads

Anyone know how much can be safely milled off the head surface to increase CR on the 1955 Caddy with 9:1 CR I be using in my 32 5w. I'm looking to increase the compression a little while going with a Isky 262/272 degree, 108 cl with .470 lift hydraulic cam, 6 deuce (97's) intake and lakester header with T5 5 speed and 3.78 quick change.

Thanks, Mike

 

.020" is safe. Anything more and the intake surface has to be milled also..

 

Thanks BOBCRMAN. The 6x2 offy intake is a two piece log ram manifold so the intake would not need to be milled like a single one piece intake. What I was asking is if any had knowledge on the maximum these heads could be safely milled. I was hoping for maybe .040" or .050".