This may be a question that nobody answers but -What are the letter codes stamped on the rear axles indicate the ratio is -78 AMC model 20 -on mine looks like either an "N" or sideways "Z" (yes I searched)

I came across a website that showed all the letters and what they mean. I do not have the web address but I wrote down all of the codes. If yours is an N it means you have a narrow track with 3.54 gears and a track lock.I am assuming this is stamped on the axle housing boss to the left of the differential cover right near the axle tube.

Check below website, it should be N which means; 3,54

http://www.jeeptech.com/wiki/index.php/Axle/Factory/Rear/AMC_20

Cool website guys-thanks!