I have a 1987 4Runner SR5 and have looked through the forums and have yet to see another first gen with the solid bench seat (vs. the 60/40 split seat). My questions is, what is the best way to add seatbelts to the rear seat that have the shoulder strap. I think this would be safer for my young daughters.

Also, the metal piece at the top of the rear of the seat, does it serve any purpose other than attaching the seat to the rollbar?

 

You should find plenty on this subject using the search. Find you a set of front seat belts, they bolt right in, same bolts fit roll bar and the floor bolt fits the hole in the side panel. Here's mine.