318 Build.. Zero Deck or Stock Deck Clearance?

You probably need to cut the deck surface to square it regardless. When I had my 318 done for my dart the banks didn't even have the same deck heights from the factory. After the cut to square deck it my JE pistons, which have a 1.815" compression height, ended up .003" over the deck. My specs worked out like this- 318 .025" over, flat top pistons with a 6.8cc valve relief, 63 cc heads (RHS LA-X), .039" head gasket, lunati 60403 cam. Static compression ratio worked out to be 9.48:1, dynamic is 8.1. I haven't run that one yet but that's less static and dynamic compression than the 340 in my Duster and it does fine on 91 octane. The JE pistons were custom made, I bought them second hand never installed. Not sure why they went with .025" over, but it worked fine for me.

So, have your shop measure the decks first! Ideally before you buy pistons. I would shoot for zero deck even with the closed chambers, you can set your compression with the head gaskets thickness pretty easily that way. And standard thickness gaskets should put you fairly close to where you need to be for pump gas on the street.