Dunno what official US tow rating is, but I'm sure it's very low.
The tow truck is 5000# with a full tank, 4.4L 2F, H55, 4.11 diff, LT255/85R16 truck tires, HD springs, etc. Trailer has surge brakes, 6lug cruiser hubs, load range E tires, 1200# empty, with a 5250# axel and max TW of 500 on the surge tongue, so 5750# gross, 4500 capacity, if maxed out & properly balanced. The parts truck is missing entire engine/trans/t-fer/d-shaft, most interior, etc, so it probably weighs 3000.
TLDR: Built FJ60 can tow 4200# with no issues.