how much can you take off the top of a piston?

[Roland Wilhelmy <rwil@sbcglobal.net>]

A friend of mine is building a 100 4-cylinder engine to M specs.  He
has new pistons, offered for that purpose, concave top.  Installed in
the block they project .030" above the block.  There is no way of
knowing the past history of the block and how much it has been shaved.

Question:  is it safe to take as much as .030" off the top of the
pistons?  If not, is getting a thick gasket from someone like Mordy
Dunst a viable solution?  If not, what then?

I will relay replies to my friend.

-Roland
BN1 my engine's already rebuilt
BJ7