Strange Dana S60 width for a body

Our 71 Dart has is 48 inches axles flange to axle flange.....tubs..and ladder bars ...15 x 10 wheels with 3 7/8 back spacing. 10 x 29 Hoosier

we used to have to deflate the 16" slicks, let the rear drop w/ the shocks un hooked to get the tires on the old hemi car back in the day--lots of ways to skin a cat !!