I got the seat belts fully installed. Now I can drive with less fear of getting killed. I also figured out a good way to make shoulder harness mounting points for the front and rear seats. Those would have to be installed before the interior panels, even if the shoulder harnesses don’t get added until much later. I also installed sound-deadening material on the insides of the cowl panels.
Somebody gave me an old set of repro running boards. They are missing the mounting brackets and some reinforcing strips, but I will probably use the right hand one, since the original right-hand running board is beyond repair.