I have used weld-on pulley hubs like you find at Tractor Supply Co. You use the size to fit the RAGB, and you can step up to 1" or 1 1/4" so you can use the same bearing for your axle and extension. If you buy the hubs with the same pulley weldment, you simply line up that end, put a bolt through the center, tighten it up and weld away. They are already keyed, and have set screws in place. Easy removal for bearing and/or sprocket changes on the extension,