Just bought a 71 and i have questions on exterior trim

[72farmer]

I just bought a pretty nice 71 with a LS swap.I restored a 72 a couple of years ago and I remember the trim was a pain.This truck needs a few corrections.The upper side molding that runs on the bedside needs securing where it stops at cab.I can see a threaded stud on the fastener that is either missing a nut or the nut needs tightening.How do you get to this nut?
Does the little center molding on the upper tailgate trim go on first or after the L&R upper molding?