My impression FWIW:
Several similar to this are out there. Not factory made, from post-1979 pickup cabs grafted onto Troopy bodies. The later pickup trucks had the vapor separator in the same spot, in the narrow area between the cab back and the bed front wall--hard to access on the original pickup truck.
A close-up photo of the joint between the bed floor and the cab rear wall would be helpful. The second and third of Kevin's photos show the curved side of the pickup cab meeting the Troopy inside wall in a curved joint--factory would've probably made a 90 degree joint to fit the seam. Also the front bed floor has been patched with a narrow piece, with the embossing cut flat at the seam that meets the cab back wall--although nicely executed, factory would likely have made a full floor for it, although the FJ43 floors have a larger extension on their rear floors, and the pickup bed floors are straight-cut at the front bed wall. Also...the upper lip of the bed walls is formed to accept the Troopy upper panels, not a utility edge-rail as seen on the pickups. Low production numbers would be the only reason for using existing pieces to construct a complete vehicle. Only the Norforce Troopies had variations from the standard Troopy body, and I am not certain that those mods were done in the toyota factory, but possibly by a sub-contractor either in Japan or another location.
Despite this, the body work seems to be nicely fit-- by someone with access to a pickup cab and a Troopy body.
Land Rover has done a similar conversion of its Defender long wheelbase 110 model into both a 110 4-door crew cab pickup as well as a longer wheelbase 130 crew cab pickup. These are/were done in their Special Vehicles division, not on the production assembly line. Land Rover has a specific rear bulkhead they manufacture to accomplish this, as well as making a true separated cab/bed pickup truck.
Likely the fabricator of this hybrid Land Cruiser had seen the Land Rover model(s) for inspiration, probably in Australia where both Land Cruiser and Land Rover existed simultaneously in fairly large numbers.
None of the official Toyota parts manuals, production lists, sales brochures shows this model exactly as executed here. I vote for a nicely done, well-thought out, one-off. Not disparaging the builder, just questioning the lineage.