The only thing about a locked AMC 20 is that the two piece shafts are a weak spot. Nice looking rig. As for the AMC rearend if the rear axle diff cover is a rounded dish style it is an original style if it has any ridges other then dents then it is an aftermarket style axle.
1978 CJ7, frame off rebuild, NV3550, Dana 300(twin stick with a sight tube), I6(258), Dana 44 Scout Axles with 4.09 gears, truetrac LSD. The rest yet to be decided.