Probably not. The Dually Fenders look the same...But the mounting lip conforms to the Styleside bed, where the Stepside fenders' mounting lip is flat to bolt to the flat wall of the stepside box.

Bought a second '86 stepside for $400, has a perfect set of rear fenders, tailgate, side walls. Took the bed, Hanging from the garage roof now, then sold the cab and chassis for $750! America... what a country!