I used a CDN spec rear seat base for the conversion on my truck.
this allowed a 2 seat belt anchor or a single middle belt and two outborad belts with 1/2 of the mounts while the other half will be on the wheel well (I am moving to this). I did not install the depressions in floor, rather I made tall front door latches (the U loops) to catch the twin seat base clasps. digital camera is at work, but I'll try to get some off. When the seat is folded forward, the U latches are the only downside to cargo space but they do run forward to rear, not side to side.
I also scored two other bases from G&S for two friends BJ74's (thanks guys)
I saw factory shoulder belt system photos, but they involve an inner roll bar system and loot like 100 pieces or so (skip that!)