There were three distinct variations (of course!) in the seat belts from 1971-1974.
The early 1971 cars used a lift-to-open latch, and the tongue was wider than it was long, with two holes in it. I honestly can't remember how the shoulder harness was integrated.
The later 1971 through 1973 cars used a diabolical setup, the same as on period Mustangs. It had a pushbutton latch, and a tongue that was longer than it was wide, with a single hole. The shoulder harness clips to a protrusion on the tongue. You have to carefully hold the tongue, attach the shoulder harness to it, then attach them both to the latch. It's difficult to do, and quite annoying.
The 1974 and later cars used a conventional three-point setup, with one inertial reel in the inner rocker, and another one screwed to the bulkhead panel near the floor, behind the seat. These belts work just like "normal" three-point belts.
Hall Pantera sells a very nice replacement setup that is similar to the last system. The latch even has a nice De Tomaso logo on it. Very nice for a street car, although for serious driving, a four- or five-point harness setup is vastly preferable.
Cheers!
Mike
