I seriously doubt "anyone make(s) conversion kits" like this. You'd need to get under the upholstery, cut the heavy steel seat frame & securely install hinges/latches. Its going to be cheaper/easier to acquire a used OEM folding seat.

The rear seat in Chateau (optional on XLT) Club Wagons for years 1992+ does fold out into a bed. Note that it does not just "fold down" the seatback is hinged to fold out at top & down at bottom, making an ~triple wide bed. There were folding rear bench seats in the earlier Econoline too.

I'd strongly recommend getting seated before you ask FORD to quote a price for the "floor mounts" & suggest a salvage yard or inquiring online for the mounts & seat.

The big hurtle may be anchoring the heavy mounting plates. Of course FORD had to do it to crash standards, resulting in the seat belts being anchored via the 8 big 'thru floor' bolts. If your "cargo model" happens to have the special threaded reinforcements under the floor to bolt into, your job is made easy. The 2 mounting plates have 4 bolts each ~17" apart front to rear & ~5" apart L to R, the rear bolt sits a bit aft of the F of the wheel well ~10" in. Suggest you inspect these areas from underneath to judge access.