Here are some stats:
...The Ring gear on the AMC 20 is 3/8" larger than the Scout II
...The Scout II has a larger contact area on the ring & pinion gearset for the same ratios (45/11 for the Scout and 41/10 for the AMC)
...The Scout II uses thicker axle tubes
...The Scout II uses 1.31" axle shafts and the AMC 20 uses 1.25"
...The Scout II uses 30 splines and the AMC has 29
...The Scout II rear drum brakes are 42% larger than the AMC 20
...The Scout II rear axle is 2" wider per side than the AMC 20 widetrack
...The Scout II uses equal length axles on each side, the AMC doesn't
...The Scout II yoke is approximately 1/4" closer to the transfer case than the AMC 20
...The Scout II uses shims to adjust the bearing preload, the AMC uses a crush sleeve, which, I have heard, can relax over time and heavy wheeling