There are different "full-width" axles, noting that the common F150 HP D44 and Ford 9" axles are about 65" wide, approximately 6.5 inches wider than the factory axles. The 3/4 or 1-ton axles tend to be closer to 68" wide, so almost 10 inches wider than stock.
I'm in the process of putting F150 axles under mine now, and have 17"x9" wheels with 4" backspacing, so I'll be about 3" wider per side than I am now with 15"x10" wheels with 3.75" BS. If I was purchasing wheels today, I'd probably aim for 4.5" to 5" BS for a slightly narrower track.