66 Dart Convertible Shoulder Belt options?

There really is no good way to install shoulder belts in a convertible that has low-back seats with no headrests, and no roll hoop. The high back Sebring seats had a built-in shoulder belt, meaning the seat was reinforced for that purpose, so that is a bolt-in solution. There are probably other non-Mopar vehicles with a similar arrangement, but you would have to do your own research. The back seat is pretty much hopeless, in that a shoulder belt would need to come up over the seat back through a hole in the convertible top well (making it useless), and without a head rest it would be a decapitation threat to the user. It would take some serious custom work to alleviate this.

My experience: I installed shoulder belts in my 1966 MG roadster. I had to swap in later model seats with headrests, and I had to fit belt guides to the headrest posts to keep the belts in place and keep them from cutting into your neck. Fortunately the vehicle already had anchor points in the rear shelf area for the shoulder belts, and there was no back seat to worry about.