Part 2 shown here just shows the seat with the cushions attached. It was a bonus that this seat folds down for access to the space behind it (if needed).
This seat is also fitted wth a 3-point seat belt system that attaches to the aircraft structure (Image 3). Again, these attach locations were designed and fabricated years ago when the fuselage was being worked on, so this was smply a matter of attaching a standard DOT-certified seat belt assembly to the mounting points. I consider 3-point seat belts a minimum safety requirement for both the rear and front passengers.
The ability to remove the seat was obviously critical, since it severly limits baggage capacity (both from a space and weight perspective). A bonus is that with the seat removed, the cargo-tracks can be used to tie down loose items with tie-down brackets that can be positioned anywhere on the tracks. Additional segments of cargo-track will be attached under the BRS chute for additional tie-down options.
It took a lot of online searching for the right seat and designing the right mounting system, but I'm satisfied with the outcome: a secure, adjustable seat, suitable for short flights, and with a 3-point safety harness.