Since you have a roll/sport bar, Any of the pickup/blazer/suburb 3 point belt systems should work. Id look for one that puts the single latch & spool (retractor) at the base of the rollbar, or in the factory position at the rear base of the seats, the roller mount up on the rollbar at shoulder height, and the female buckle inboard of the seats. Just make sure your rollbar is mounted solid and reinforced well if you plan on tying your body to it.
http://67-72chevytrucks.com/vboard/s...light=shoulder