HOW TO REMOVE THE SEAT BACK in a wagon;
1. Easier if you first remove the seat bottom using the lever on driver's side.[easy]
2. You must be able to release the latch to get the back to fold to about a 30 degree angle. Carefully use a small screw driver to release from each side - trial and error. You may be able to remove the latch bracket from the sides with an angled screw driver
3. Carefully remove the upholstery hog rings along the bottom edge of the seat back. This will expose a galvanized metal support that runs the length.
4. About 3 inches inboard on each side there is a hole about the size of a nickel in the galvanized piece referred to in #3.
5. Starting with one side, insert a thin screw driver with at least a 6 inch shaft into the hole. You are going to push a spring-loaded rod OUTBOARD which will release that side from a bracket located on the wheel well. Movement is about 1/2 inch. The back pivots on this rod. [The spring action of the rod pulls inboard into the bracket on the wheel well]
6. Once you have released one side, put a rag on the bracket so it doesn't slip back into the bracket and repeat the process on the other side. Also, once released be careful not to let the rod tear the upholstery on the wheel well.
7. Lift the seat back out.
8. If you get a back with a metal release from a pre-86 [I think] the upholstery from your seat can be transferred to your "new" seat back.

Hope this helps.