I'm trying to figure out a similar problem. I'm waiting for confirmation on the original width of the rear axle on my '53 GMC 100. From what I know, there are several rear ends from GM/Chevy that had a 6 lug pattern but may be too wide. The Colorado/Canyon also runs a 6x5.5 bolt pattern and I am looking into that diff. I also believe Nissan and Toyota have diffs with that bolt pattern.
