Having Dana 60 cut for my 72 Duster

The 1 3/8 is not the pinion offset. It's the difference in tube lengths to get the proper pinion offset.

Like I wrote, if you have a SBP set up now or bbp using redrilled sbp drums, BBP stuff will push your tires out about 1/4" on each side. If it's already BBP using the larger drums, then cut it at 52/58.

I have an excel spreadsheet written that calculates the axle tube lengths and required axle lengths for both D60 and 8.75's. Shoot me a PM with an e-mail address if you want it.