Finally following up on the seats. They are indeed from a Toyota. I can't find any indication of model/year, though.
Here is the lower frame:
I pulled the seat out because the seat-back was sitting crooked...it was pretty noticeable from the back:
Apparently, the clearance with the tunnel was tight on the right side of the seat, so they lower side frame was trimmed. Too much apparently, as it had bent severely:
I was able to partially straighten that on the workbench, but still not perfect. Will take it to a welding shop to get it reinforced. Maybe they can straighten it more...or maybe I should try again myself before taking it for reinforcement.
I don't know if the base brackets are from the Toyota or if they were custom made to fit this Wagoneer. They look nicely made, from 1/8" steel, but I found no part# or any other stampings on them, so I suspect custom. I also noted what looked like angle-iron welded to the seat frame with the sliders attached to that. I should have taken more pics...sorry. If I take it off again, I'll do better
There are studs protruding from the floor for 3 of the 4 mounting bolts. The 4th (back left) has a hole and there is a square nut welded into the frame:
The location of the other 3 - I could not see them from under the car.
77 Wagoneer and 97 TJ.