Seatbelt question: What year required shoulder belts?

I believe mid year 1968 is when shoulder belts were required for front outboard occupants. My 69 has spots for rear outboard shoulder belts. Slots in package tray sheetmetal. The rear shoulder belts appear to be a really rare option on 69.

Buy a set of wesco performance lift latch shoulder belts with upper sash and retractor mechanism and 12" long end with buckle. Forget about the OEM stuff. It was a pain in the ***.
Right now, I'm thinking about getting a pair of Sebring convert seats with the built in harness. The buckets that were in the car are really nice.. the problem with that is I'm a smoker, and I want this to be a fun car for me, so I'd rather not smoke up or burn those nice a-body seats.. save them for the kid or whoever has this car after me. But I'd like to have the setup ready to go back to those seats with decent belts.