When you measured the head did you put clear platic + grease over the combustion chamber for an accurate measurement? 0.8 will not give you 7cc, 86mm diamiter at 0.8 height gives you 4.6cc, so it will probably be 4cc by the time you equate for the sqish zones.
I asked Rodgers to take 4cc out of Steves RB20 head (stock head is 40cc), and he wouldn't do it. He would only change the deck height on the block. He will be able to sort the piston though.
I can't see valve clearance being an issue with the design of the rb30 piston, what is the volume of the piston dish?
Use brake cleaner to test the valve seal before final reassembly, If you used it now it'd be alike a tsunami coming though.