“Mechanically, the Grand Wagoneer was a hodgepodge of different OEM systems scrounged from wherever AMC could find affordable parts.”
That is so untrue, but oft repeated about AMC!! Yes, they bought A FEW items from other manufacturers, but you can count them on one hand. The only big item they purchased was the transmission. Carbs and electrical systems (starter/alternator) were purchased, so was the steering box and column. Other than things like switches that was about it, and all the manufacturers bought small items from outside sources. The general criteria for “build it or buy it” was if they could buy it cheaper than develop and build their own, they did. Half the components of a car are bought from outside sources now (might have been designed in house though, then sent out for bid with those specs). AMC pioneered that! The big three sold to other manufacturers as well, such as GM selling auto trannys to Rolls Royce. Jaguar used Borg Warner autos for the longest time.
The interesting thing about the FSJ Jeeps is that the body is essentially the same from 1963-1991. If you pull the plastic grille off you will find the exact same sheet metal underneath as the 1963 “Rhino” grille models. In fact, you can cut the tabs off AMC added to install the plastic grille and put an old Rhino grille and rounds headlights in (change the headlight buckets)!! Except for some trim and maybe mounting holes, body panels interchange 63-91. One of the longest runs of a body design in history! The Volvo 2xx and VW Beetle have it beat though… but definitely longest SUV design! I briefly thought about building one for a camper tow vehicle. It really needs a modern engine and 4-6 speed auto trans though. The three speed and smog era engine really hurt it. It’s easy enough to improve engine efficiency and power – it’s the same old AMC 360 many AMCers race with – but harder to mate a modern trans. I’d have wanted reliable EFI too, which as noted is around $3K to add. So I’d have bought a salvage yard Ford/Chevy/Chrysler EFI engine and trans from a late model truck or SUV. If I REALLY loved the big Wagoneer I’d have spent the $10K or so to build it (I’m a decent fabricator and hot rodder), but I don’t love it that much. Bought a good late model SUV (Expedition) for about the same price instead, and don’t have to wait a year or more to drive it.