The gap from the radiator to the WP pulley is under 4" for the original thick radiators, you must have the later half depth one yes? I've read here of members thinking it would work with that one, but I guess it's just a little too thick.
I bought the same Flexlite 180 fan that Cobra** used for his truck. He has a thread here showing how he made it fit, and those fans are pretty good.
You might be able to fit one of the Taurus fans with the shroud cut down a lot, but I wouldn't bet on it without seeing it done first. I had bought a used Mark VIII and Taurus fan before someone knew if they would fit(the thick radiator).