I put in a new axle in my 56 1 1/2 tone with rear disc brakes. 10 lug pattern same as the original. Went from a 6.17 gear ratio to 4.63. Spring pad difference was 3/8" overall center to center so I open the alignment hole 3/16" on either side to fit. The axle I used was from a 2001 HD3500 truck. I drove it a couple times and the brakes functioned just fine. I did keep the hydrovac in and put in a new stock MC. I put in a residual valve going to the rear discs. The axle tubes are the same diameter as my stock axle so I reused the part that clamps to the axle with the U bolts and has integrated shock mounts. I did get new U bolts for it though as recommended. I have drum on the steer axle still, but have acquired a stepvan and took the front axle for the disc brake swap that Grigg described in another post. I also kept the rear axle because it was in great shape, longer gears and disc as well. Thought someone could use it for a swap too. It's a Rockwell Model C with 5.29 gears.
