Although I don't recall ever seeing one, a front bench seat was standard equipment in '78, so it's possible to put one in your '76. Since you'll not likely ever find a stock one you'll have to go to the junkyard with a tape measure and find something that will fit. Probably the second seat in a van or mini-van will work. Then you'll have to make your own mounts.

There really isn't room for middle-facing seats in a CJ. Just try sitting on the fenderwell and see where your feet go. You might be able to put a single seat there facing one side, but I think it would only be suitable for kidlets.