You most likely have the Dana 44 Twin Traction Beam (TTB) It's that goofy tire eating, semi independent front suspension used by ford for decades.
A Dana 60 is what you probably want. It's a beefy straight axle, and the one you want is found on one ton fords. As how to identify it, I am not sure.
Some quick research shows that a Dana 61 is a variant of a Dana 60. As far as I can tell, it has mainly internal modifications with an offset pinion to allow the use of lower ( numerically speaking) gears. A Dana 60 would be your best bet. They come in gear ratios that are compatible with your truck. It sounds like the 61 is only available with low numbered gears, i.e. 3.07.