The early versions of the XLR-350 used a Fasco D326 front mount motor until 1983.
After 1983 it switched to our standard 522004 convection motor.
To replace the Fasco motor you would need the following parts as long as your existing convection system has an 8" x 8" fan plate that unbolts from the liner.
Early models that do not have the 8" x 8" do not have a retrofit solution available for the convection motor.
591002 Fan Motor Mount Plate Bracket
073005 Fan Motor Mount Plate Gasket
084001 Insulation Board
512005 Convection Motor Wall Plate / Inner Plate (goes on then then insulation board goes on then fan mount plate goes on)