I won't machine the heads into open chambers...lots of $$$ and the effects probably aren't good as the castings aren't designed for that.. I'd much rather spend the money on custom zero deck pistons than that.
With a thick enough head gasket, the pistons sticking out of the deck is irrelevant. I know it would work at 0.040+, just wondering if the 0.005" tighter clearance is a make or break dimension.