Tonight I removed the remaining clecos from the holes in the skin that were holding the rear baffle in place while the tank sealant was setting. These remaining holes were the ones that the instructions said to leave without countersinking so that the clecos would have maximum holding strength. So these holes were countersunk to allow flush rivets, and those were then hand squeezed in.
What's next? Both fuel tanks just need their fuel senders to be installed permanently with tank sealant and screws.