Well, if you can find the piston info on the build info, that would be imporant to complete the picture of what you have. The reason I question that it is a 'stock' 340 bottom end is that the stock 340 pistons stick up about .018" above the deck. The Speedmaster heads with 64 cc chambers (assuming that is what they are) are closed chamber heads. You would need a thick head gasket to keep the heads' closed chamber area far enough from the pistons to keep them from hitting each other; a standard Felpro head gasket would juuuust be barely enough and we don't know that it was used or something different or thicker....or thinner, in which case you may be skirting disaster.