My pickup had originally been a flatbed and the gas tank is under the front seat. The back rest is hinged at the top just below the rear window. The bottom seat is hinged at the rear and the hinge has two sets of caged nuts (a total of 3) to adjust the forward and back position. The back rest has a 1 x 3" board hinged at the bottom of the rest, and when hinged up the back rest is all the way back and when hinged down puts the lower portion of the back rest forward 3". This sounds confusing, I hope it is clear to you. I saw a 1938 pickup a few weeks back and that had a post about1" high in each front corner of the lower cushion. The seat frame had 3 holes in it and moving the seat to the prober hole adjusted the lower cushion.