I'm sure it can be made to fit.
I could be wrong, but I thought all the 4 cylinder Rangers got a 7.5 diff, but maybe by '99, they had abandoned the 7.5. A 4.0 always had an 8.8 diff behind it from the factory.
I don't know for sure how well a 7.5 would hold up to a 4.0. If it is a 7.5, I think I'd pass and keep looking for an 8.8 to put behind that 4.0 (preferably an 8.8 from an Explorer which will have the bigger axleshafts).