Ian, no you don't need and should NOT remove the Allen bolt on the outside. Has I said all you need to do is move the motor/gearbox unit away from the flange of the "mover". As said its a simple three bolt fixing. That will allow the roller to come off the outside bearing journal. Then you will find you can move the roller to one side enough for the roller to come towards you. In moving towards you the inboard end of the roller simply comes of the shaft of the gearbox.
The "drive" by the way is taken by a "rollpin" diametrically through the gearbox shaft, onto an open-ended slot in the roller. That "rollpin" stays in place. Put some grease on that gearbox shaft/rollpin on reassembly to stop corrosion and make the drive less harsh, less prone to knocking. Don't grease the out board bearing its only a plastic shell and grease will cause dirt to stick in there and wear it away quicker; its a dry bearing.