I figured out what was wrong with the latch; the screw & nut I used was too tight and didn't let the cable relax on release. I loosened the nut a bit (nylok) and now it swivels and the pins retract well. I still don't like the design, but I need to move on and not try to re-design the kit (although I see that TAF has a new latch now.)
I finished the seat bottom and riveted it closed. I then assembled it to the hinge on the seat back in the same manner I did before, putting the hinge under the skin for a flat lay and nice finish. Finally I riveted the assembly together and it folds nicely.
