I looked into it at one time. Couldn't find a decent donor set of seats.

The seats will bolt in. Your existing lap belts will work. If you want shoulder belts a kit is available from the dealer ($$) and you will need to get the side panels to use the belts. You will need to acquire the striker on the passanger side to lock the passanger side back. The bosses are already there.

SR5 trucks in 1985 did have split seats. What color you looking for. I might know of a gray SR5 4Runner getting parted out. It had a split rear seat. Don't know if it's still there.