Thanks Mike, I am imagining a similar experience with this swap. Once I get the doner scraped clean of the built-up debris I can get a better measurement between the mounting bolts, mine is pretty clean 'cuz I replaced the pinion seal a few years ago and power washed the axle before hand. For now it looks like it should match, I'm going forward with it and will report back with the results. I think my driveshaft length is fine, same dimension from the center of the U-joint to the center of the axle housing and mine is a three-shaft truck with a slip-joint on the rear shaft. I did what you did, drew a picture of each with bolt spread dimensions, I think they are the same. We will all find out as I progress.
