FJ80s had optional front and rear E-lockers, not just rear. There were also coil springs front and rear on those.
The axles are different from mini truck axles. Generally stronger with a larger ring gear and larger birfields I think.
These days, though with the availability of aftermarket shafts that put mini truck axles into dana 60 (stock) strength, its not much of an issue. The 8" R & P is pretty stout, too..
FJ40s ran a 4.2 liter straight siz, I believe. The origianl designs were done in the 50s when Japan was in reconstruction and many things were provides from our industry. Those motors are almost a clone of the Chevrolet inline six of the era...