Optional was a 4.11/1 ring and pinion set. Rare as heck today. But a reproduction set is available from Chuck Mantiglia at Chuck's Trucks. I have his sets in my front and rear, but am not on the road yet, and know of several others with the sets in operation who are very happy with them. Chuck's site below. Stu
http://www.chuckstrucksllc.com/startframe.htm