I believe it's: 3.07 in a 12 bolt, 3.08 10 bolt.
3.31 in a 12 bolt, 3.36 10 bolt.
3.73 in a 12 bolt, 3.70 10 bolt.
see: http://www.chevellestuff.com/generic/axlecodes.htm#1964
and compare to other years that had both 10 and 12 bolts available.
Only after I get done typing that I find this!http://www.chevellestuff.com/generic/axlecodes.htm#10-bolt%20vs.%2012-bolt%20ratios Pete Geurds Douglassville, PA
