76-77 Broncos are roughly 2.00" wider in the front. Later model Fords, Chevy's and Dodges are up to 3" wider front to rear.
It has to do with Ackerman angle and turning radius. I wouldn't worry about it. With that said, Ackerman angle is not really that important on something with a lot of tire sidewall and on something that does not handle very well.