I have a line on some 55 series axles with disc brakes (on the front anyway). I imagine that they should swap easily over to my 74 40. Might be an inexpensive way for me to get discs. Are there any problems that I might run into doing this swap? It seems to me that it would be the same as swaping in a later 40 series axle. Should I swap in the rear axle at the same time? Are they any wider? Thanks.