RE Juliano's: You don't need to drill and install a rivet, that's crazy. Why not install the D ring, belt and bolt while holding it up with the yard stick? Why put the bolt in without the other stuff, the plate can not rotate. Juliano's was not thinking. They also have the instructions out of sequence and don't say why there are three holes in the shoulder belt mounting bracket.(different application probably). As far as putting brackets all the way across and beefing up the belt mounts. There are differing schools of thought on what is safe there. Seat belts on old trucks are tricky. The seat mounts are not safe to begin with and will tear out on a good impact. If you make the seat belts real strong and the seat mounts shear/pull out of the floor and seat moves forward, you are sandwiched, strangled or injured if you hit the column. With no air bags and no collapsing wheel or column, one may want to strengthen the seat mounts also. Later years were designed so that seats do not break loose. The shoulder harness then kept you from chest injury and then air bags were invented and all the rest. Just call me "Happy thoughts" Bartamos.
The reason for installing the rivet is so that the plate stays in place on its own if you ever need to remove the belt. Do you want to re-do the yardstick procedure every time you have to take the seatbelt off? Say you want to repaint or need better access to this area, it's simply remove one bolt and replace it when you're done. Juliano's WAS thinking. It's an easy and simple way to make the plate more permanent.
I agree with you that mounting to the seat isn't the best, unless the seat is very well secured in the floor.
