Those aren't technically domed pistons. They're flat tops, with valve reliefs and an obvious bevel around the top edge. The 7.5 cc's should take the valve reliefs, recessed circle in the middle, and perimeter bevel all into account. I could be wrong, but I believe you'd enter the 7.5 as a positive number since it's added volume. The amount that the flat piston surface is above the deck should be entered as a negative number. You did it right in the calculator posted in post #46. Just adjust the piston volume to 7.5 instead of 8 - which won't move the needle much.
If you're deck height is actually -0.030", you're going to want a thicker head gasket than 0.039".