It would work, but it's going to be narrower than his rear. You also want to make sure that it IS from a fj60 and not something earlier. Does it have disc brakes? I'm not sure about spring pad width, but it's not going to matter much since you're going to have to fab mounts anyway. Unless you buy a spring hanger kit, then you might have to move the perches. But that would also give you the opportunity to cut and turn the axle too.
It's also going to be heavier and have a little less clearance, but not really huge concerns. The other down fall is that if he carriers spare parts, the front and rear diffs will not be interchangable.