While you're there, don't rivet in the floor until you fab and fit all the fuel/vent/cables/stiffeners/heater box + center floor cover - anything where it would make access easier to walk up/duck under to the center section, with or without the firewall in place. If you build right side up, also fit the floors, flap actuator, finish out the baggage area, and so on. Life is so much easier if you don't follow the plans order. When you're ready to install & rivet the floor, first rivet the two center stiffeners to their end brackets and firewall angles, then position the floor.
John Siebold
