Deburred the lower skin aft-to-fwd fuse mate joint tonight.
Removed that edge of the aft fuse skin, because popular opinion is to leave the skin completely off until just before airworthiness inspection.
Reassembled the fuse side panels to the aft fuse. Installed the upper / lower firewall crossties. Positioned the lower skin into position and cleco'd.
At this point I stopped to think about things. The firewall stiffener brackets are hard to get to once the firewall is installed, so I positioned and cleco'd those. Will not install fhe firewall until after they are riveted.