hey gene try this it covers a lot http://www.chevytrucks.org/tech/rear_ends.htm http://www.chevytrucks.org/tech/ifs&rearend.htm this has some good info. the 55-59 trucks are closer to 61 1/2" wide. caprice/cop car 10 bolt is 62" 3.08 and 3.42 with positraction is common. i am working on a 56 stepside. 71-81 camero trans am seem to be one of the most common swapped rearends it is real close in factory width after varifiying for myself. hope this helps some.