I have used steel shim gaskets with aluminum heads, and no issues. Sealed them with Copper Coat. I know a guy in England that used them on a 383 , alum heads, he drives his RR everyday and no leaks. Sealed them with Hylomar. It really isnt recommended, but some guys get away with it. Since you have a choice at this point, i would do as Jim said, deck the block for zero clearance, and use a .039 composition gasket that's approved for use with Alum heads. Then you'll get some good quench too! Check out the UEM COMPRESSION RATIO CALCULATORS, for quick answers on C/R
