From the research files:

The Ranger rear has an offset pumpkin and can be narrowed to the proper 544 size by cutting and welding the "long side" housing to the same length as the short side and swapping the long axle for another short axle. 85-89 Rangers used 7.5" gears, '90 and up used 8.8" gears. Limited slip very common. Aerostar vans also had the centers offset, but to the other side, so that's a candidate also.
More info here:
http://www.therangerstation.com/tech_library/Axles.html

Bob Melville (the Canadian guy who had 5.0 liter Ford put into a 544, used a rear from an '87 2wd S10 pickup. His notes say 2wd only! I'm not sure why. Supposedly the overall width is the same as the 544 but I would guess that the lug bolt pattern would be different. Seems like changing the bolt pattern would be less work than cutting and welding axle housings. It's also a 7.5" rear, commonly available with posi. Another link....
http://www.h-body.org/people/projects/building_lt1/vega%20conversion%20tips.html
A ways down on the page is where the usefull info starts, under suspensions...

Happy reading!
neil