This is one way to install fullsize rear axle

The rear axle is simple but keep in mind amc drivetrain is offset to the drivers side making the pasenger side axle tube longer than the drivers. Now the rear can be installed by cutting the old purches off and re welding them 76-86cj's 36 inches apart. Dont forget the new axle may take a different size u joint, dont worry they make ujoints with custom ends that arent much more than standard sizes (meaning you can have 2 sizes different than the other 2 on a 4 end u joint). Upgrading from that AMC 20 isnt a bad idea and even from a dana 44. but remember this might make your jeep illegal for use on the road without the right fender flares, LETS KEEP IT LEGAL!!!!! hope someone gets help from this