[valiant67]

Welcome!
Since the cab didn't really change much even into the 90's, if the later models anchor the belts there you should be good. As I understand, the anchor points were built in before the belts were required (or may have been an option).

 

[valiant67]

It might be worth considering factory seat belts from a junkyard if you could find some in good condition that aren't worn or subject to the stress from an accident.