It's great you caught you mistake, congrats!!!!! Gonna ask the question of why do you think you need to buy new head gaskets? If they are not torn, or other wise damaged, they haven't gone thru a thermal cycle, I'd bolt them back down and go!
YIKES! I've heard of stop when it sounds expensive, but usually people are joking...that's just ugly!
I got my block and rotating assembly back from the shop, balanced, assembly washed and ready to assemble. I got 7 of the KB pistons mounted , ringed (yeah, gapped the rings) and found the eighth piston was a clone of the 7th. They are a older set of the 107's. So I have that on the shelf now and a new one in it's place. The new one has the same flycut for the intake and exhaust. They're trying to save us from ourselves..