is it possible to put a shoulder/lap seat belt in my duster?

I would first post on this site under the parts wanted Forum.

I have a 72' Duster that has both front seat lap belts and shoulder belts (not for sale). These are separate belts that you connect together. You might want to check out e-Bay for some new or used seatbelts. They may have old ones and/or aftermarket belts available.

I would guess that at least some 73's were offered with both since the 72's had em. Good Luck.