For what it's worth, I just recently switched the rear axle in my 62 1/2 ton.. Had the stock 10 bolt pumpkin with a 3;90 R&P.. Owch..!! Was afraid to drive it past 50 miles an hour with that 235 motor screaming..!! So my friend had a 12 bolt axle from a 69 that already had a 3;07 R&P in it.. It bolted right up like it was made for it.. Best thing I ever did.. The parts for the later model 12 bolts are easier to get and also they are easier to work on.. The only thing I had to do is re-set the welds on the brackets and make sure those wheels were set plum so It would track properly.. But you'd have to make sure they were plum anyway even if you were swapping out the same axle for the same axle.. Point is, it was easy peezy japaneezy..
Longbox55 along with some other guys on this forum coached me through the whole thing..
Thanks guys..
