How about some more info too? Such as, how much lift is on it, and what other modifications have been done?
Was thinking the same thing about it being a '77 and having so little positive caster. Wondering if the alignment sheet is showing it incorrectly, or even if someone in the past swapped out the front end for an earlier model. After all, most earlier Broncos had precious little caster to begin with. But by '77, most of them were pretty good.
Mine is at 6 degrees plus, with 2.5" of lift and just C-bushings. Can't remember what degree, but the point is that with the same setup and 2" of lift, my '71 had zero degrees. Or something like that.
Have you owned your Bronco for a long time? Or is it new to you? Does it still have factory style disc brakes up front? Would not be the first time someone swapped in an older 44 for the later one with disc brakes.
When you get a chance, post up some pics of your alignment readout, let us know how much lift you're running, and anything else you can think of.
Besides, we love to seep pics of "stuff" and especially Broncos!
Good luck.
Paul