Im using a 12 bolt out of a 78 chev suburban. 6 stud. Also 3.07 ratio. I made up blocks for between diff and springs that match the offset of the stock set up. You will notice that the center off diff housing and spring center bolt are off set. If you dont do that the diff will be to far forward and the tires may not fit in fender opening very nice. If you use the 56 thru 59 housing get the springs from same year. Or change the springs to the 56 thru 59 springs and use a newer diff. The spring center bolts are in different locations after 54. The difference between torque tube and open drive line. Hope that makes sense.
