Keb88 your 57 has 12" brake drums and all the 6 lug drums I have run across are 11" about 20 years ago I changed a 55 2nd 3600 to 6 lug but I changed the whole axle assembly I dont remember if I did this because the spindle was different or if it was because the the other axle Had better king pins. you could use a mic and measure the spindle on both and see if you could modify the backing plate to fit. hope this helps
jim