I had this exact van, but a 92. Same Chateau interior, white/tan paint and 460. It's hard to believe he's found one of these with under 100k, but if he has more power to him. Keep in mind it's got a very aged e40d trans if it hasn't been rebuilt. Also, it is indeed a gas hog. My 25' v10 motorhome gets about 2mpg more than both of the 460 vans I've had. Expect about 9 MPG, and it ISN'T going to get better no matter what he does. That's what they get. If he isn't comfortable with that keep looking.
As for the conversion, I haven't seen a Javier van without an extreme 6" or more lift on it. The modest stance of this one makes me think older Quigley but I can't see any radius arms either.
I'd agree with above that the van is worth 5-15 at the very most. Probably a good deal at 10 if the 4x parts look and drive ok underneath. The older 2wd Fords (92-96) were horrible at handling in 2wd form. All over the road, every one I've driven and that's a lot. 4wd conversions have usually had the wander and horror worked out of them but I'd be giving it a good test drive in all conditions if possible.