Purchased D4d, it is a 20j model. Turbo, direct drive SA cat. Looking at my books I see that the 20J books are just additional info to the 78A books. Was the 20 J the special application version of the 78A? Or was it produced after the 78a run was over? I thought the 20j was replaced by the 84J series. Does any one know how many 20J tractors were built? Thanks, Mike