Thanks Ted and everyone for the comprehensive explanation regarding milling cylinder heads and blocks. When I rebuilt my engine about 11 years ago it was quite difficult to fit in place the valley cover and also the intake manifold barely clears the valley cover. That's because I didn't  take into consideration the added thickness of the composition head gaskets.    .023" was removed from the decks and .010" from the G heads for a total of .033".   So, .033 X 1.4 = .0462    The machinist and I didn't feel comfortable milling that much stock from the intake surface of each head so only removed aprox. half that figure give or take a couple.   In reality, there shouldn't have been any stock removed from the cylinder head intake surfaces at all.  If I rebuild another Y-block engine, I will seriously consider custom pistons by adjusting the compression height accordingly and remove only  enough deck metal to true it up. I will admit I have no experience ordering custom pistons though. There has been no issues or leaks other than the valley cover being very difficult to install with out distorting it.  The pistons in this rebuild were cast Silvolite and the final dimension being .010 in the hole.  



64F100 57FAIRLANE500

If your pistons are .010, and your head gaskets have a compressed thickness of ,046, your quench is .056, just barely short of the recommended maximum of .060. 

If i remember reading the teds article correct you take the distance removed from head, deck, and gasket subtract .035 and multiple whats left by 1.4. using teds example: .065-.035= .030 x 1.4= .042.  your nearing the point where mill the intake would be needed but not yet there.
seth