shaved J heads

I saw in a 415 hp 318 build in engine masters they shaved some smog heads down .050 and ran it with stock pushrods and non-adjustable rockers, with a pretty big comp cam. I called comp and they said it's not a problem. Now, that seems pretty wild to me, but if I were to shave say, .040 off and use some 273 rockers it might be pretty good? Can anyone tell me with a stock 318 .039 gasket, and 70cc J heads if I have em milled .040 what cr would I end up with?