Just in case you were wondering on the same info i am:
Dimensions Wheel mounting flange-to-flange
Front axle - 79 1⁄2 inches
Rear axle, single wheel configuration - 69 1⁄4 inches
Rear axle, dual wheel configuration - 79 1⁄2 inches
Centersection: Double reduction-style - The upper ring-and-pinion gearset drives an intermediate gear that, in turn, drives the big, gnarly bull gear. The differential or locker is housed inside the carrier sandwiching the bull gear.
Upper ring-and-pinion: 22-teeth on ring gear, 9-teeth on pinion = 2.44:1 Lower bull gear and intermediate gear: 33-teeth on bull gear, 12-teeth on intermediate gear = 2.75:1
Final gear ratio: 6.72:1 (combination of 2.44 ring-and-pinion and 2.75 lower gear)
Axleshaft: 1.62-inch, 16-spline
Differential: Open four-spider gear design or Detroit Locker (PN 225S-15)
Bolt pattern: 6-on-8 3/4
Rockwell Weigth & Weight Saving Options
Rockwell 2.5 toploader Front Axle - 670lbs
Rockwell 2.5 toploader Rear Axle - 500lbs
The above weights are with no brakes or backing plates. You will save ~80lbs per-side by removing the drum brakes. Replace the factory HEAVY brakes with light pinion brakes or wheel-mounted disc brakes.
For reference a chevy dana 60 front weighs 516 lbs
Steering
The stock deuce steering arm is held on by four bolts similar to an early kingpin-style Dana 60. You can find steering arms or full hydraulic steering kits.
Shaft Comparison
Shown from left to right are: a 1.31-inch, 30-spline Dana 44 axle; a 1.5-inch, 35-spline Dana 60 axle; and a 1.62-inch, 16-spline 2 1/2-ton axle. When narrowing housings, you must use either stock shafts or custom shafts. You can't just cut and re-spline a Rockwell inner shaft because the shafts neck down in the middle.
U-Joints
Shown from left to right are a Dana 44 U-joint and shaft assembly, a Dana 60 assembly and a Spicer-style Rockwell assembly. The Spicer joint measures a monster 5 1/16 inches from cup to cup. The cup diameter is 1 5/8 inches.