Looking to buy/build 500-600 fwhp 360

MopaR&D said
Attaining 'true' zero deck on the pistons would require measuring what the current block deck height is, the older LA engines were pretty bad about the decks being taller than spec but a Magnum block is going to be a lot closer to what it's supposed to be. The kit you got has a note at the bottom of the page, "calculated using a zero-deck engine with .030" overbore and .040"-thick head gaskets". When you go and install the pistons they may end up being .005-.010" below deck or more which will affect (lower) your actual static compression measurably.

Surely there must be a way to check for deck height before assembly. I'll have to do that, because we might as well try for maximum compression on pump gas. I've kind of resigned myself to milling the cylinder heads to reduce the chamber volume. I don't think milling heads is very expensive. We can just mill the block to make sure we have zero deck height, but the kit does not show flat top pistons. So how do you get a zero deck height when the pop up piston is sticking up proud to the block?