F09-01 Aft Lower Cabin Detail Installation.
I located, Pilot Drilled and Clecoed:
F09-02 Seat Bet Attach Assembly,
F10-24 Gusset Plate with F10-25 Gusset Spacer,
F10-02 Cap Assembly, and
F10-09 R&L Support Channels.

For F09-02 Seat Belt Attach Assembly and F10-09 Support Channels I used a line drawn on the flange to line up with the holes in the lower skin.

I also clamped the F10-02 Cap Assembly to the F09-02 Seat Belt Assembly to be sure that there was a constant height from the lower skin.

Click on a picture to enlarge it: