Rear Axle Length
I think Cass did this you'd need to adjust it slightly for the 1.3125 offset you have versus the 1.375 in the example:
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Stock pinion offset, driver's side tube and axle is 1 3/8" longer than passenger's side.
Typical truck Dana 60 casting: 17.5" wide
Assembly width: 51"
½ housing offset measurement = .6875
Housing width: 51 - .125 - .125 - 2.4 - 2.4 - .125 - .125 = 45.7"
Tube lengths:
45.7 - 17.5 = 28.2
28.2 / 2 = 14.1
14.1 - .6875 = 13.41" total pass side length
13.41" - housing end width = Passenger's side tube length
13.41" + 1.375 = 14.79" total drivers side length
14.79" - housing end width = Driver's side tube length
Most Dana 60 spools and all 35 spline sure-grips use 30 degree pressure angle and 1.75" axle end gap.
Axle specs:
5 x 4 1/2" bolt pattern
2.830" center register
2.5" axle flange to wheel bearing journal (step)
6" axle flange diameter
MO-400 or ST-400 Green wheel bearing
Axle lengths (overall length, flange to end of spline):
51 - .125 - .125 - 1.75 = 49"
49 / 2 = 24.5"
24.5 - .6875 = 23.81" Passenger's side axle length
23.81 + 1.375 = 25.19" Driver's side axle length
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If you took .20 off each of those axle lengths, you're pretty dang close to yours.