If you have a 258, I know for a fact a tuarus electric fan out of a car with a 3.8 engine will work perfect. It is two speed and readily has enough power to use as a primary fan
It is a rather "trendy" swap on Pirate 4x4 right now.
I have not tried it in a fsj, but in a cj, and if I can fit it in my CJ, where I have less than 5 inches between the water pump pulley and the radiator, I know you can fit it in a FSJ.
Check out Sore4x4.com
for a 4x4 site local to SW Washington/Oregon!