Rear Seat Question

[Bino]

So my Blazer didn't come with any of the original seats when purchased. I've been collecting original core seats and slapping seat covers on them in the short term. Today I was installing the rear seat and noticed that the mounting doesn't really line up. I notice every picture on the board has 4 brackets across the back of the rear seat, the seat belts also mount to these. My seat has two brackets... pics attached... You can see that the brackets do not line up with any of the mounting locations. I'm thinking this may be a '69-'70 seat... pre-seat belts?

I'm also looking for seat belts for the rear (preferably black)... If anybody has some laying about.

As always, much thanks