All AMC 20s have a 8 7/8" R&P and use a 29 spline shafts. The AMC 20 R&P is 3/8" bigger than the Dana 44, but it uses smaller shafts, smaller axle tubes, and the CJ version comes with weaker two piece shafts. The AMC20 uses a 29 spline shaft where as the later Dana 44 uses a 30 spline shaft. The AMC 20 housing tends to flex a lot which can cause breakage. This can be remedied by welding the tubes and/or adding gussets. The reason the AMC 20 flexes more than the Dana 44 is the shorter differential housing and smaller axle tubes. It's other flaw is the CJ version uses the two piece axle made up of a hub and a shaft. The hub end tends to break off under load which has created the market for one piece AMC 20 axle shafts. Unfortunately, the shafts are expensive ($350+ USD) and in some cases a special bearing must be used.

The CJs used two versions of the AMC 20, the narrow track from '76-'81 and the wide track from '82-'86. Both versions use keyed, two piece shaft/hub design and 5 on 5.5" wheel bolt pattern. Supplies of AMC 20s were exhausted in 1986 and some Dana 44s were used instead in the last of the CJ-7s.

From 1976-1978 a larger 11x2" drum brakes was used on the AMC 20. After 1978, a 10x1.75" drum was used.

The Wagoneer and full size Cherokee also used a narrow and wide track version of the AMC 20. Both SJ versions used once piece shafts and 6 on 5.5" wheel bolt pattern. Since the length and bolt pattern is different from the CJ version, the SJ shafts are not compatible without resplining and redrilling. I've never heard of anyone going to the trouble.

They're two piece shafts even in the Javelins, so it's likely 2-pc shafts in all oem applications. I've read that loosening the bolt a bit then tightening to spec (not sure so not sayin) every so often will prevent breakage.

I swear I saw one of these in the junkyard the other day. Maybe I'll try to save it.