YJ dude, sounds to me like you have an early Dana 35 non "C" clip axle. The axles are not interchangeable. But if the housing and axles are in good shape, you may be able to swap carriers and replace the ARB with your EZ locker.
How bad is the ARB? You might want to contact the ARB folks in Seattle to see if it can be salvaged. I've seen some ARB's in rough shape that were put back together with the help of the ARB people. Good group to work with. The non "C" clip housing is worth saving, especially if you have Summer bro. axles.
'91 YJ, 4.0L 5sp, Atlas II, RE SOA + 2"BDS, 35" Explorer Xterrains, ARB's & 4.56 gears, WARN 9000i