Just bought a mint condition '90 cummins ram 3/4 ton with a 1 ton rear ax. Just bought dually fenders shipped from maritimes, "supposed" to fit "250" box. Shipper now says "250" single axle box probably can't be duallied, as a dually box is needed. This is apparently based on info for a "350". I do know that I will need spacers, but does anyone know anything about single ax and dually ax "box" (8') differences?