how can i tell if my 79 cherokee has D44s or amc20s

 

Unless someone did an axle swap, all 79 full sizes had a D44 front as far as I know. The D44 rear will have a diff cover that looks just like the front one, with contours in it. The AMC20 diff cover has a very smooth diff cover, like a bald head.

You could post pics if you'd like. Also, search google images for either axle and I am sure you could come up with comparison pics.