Unless you plan on racing the car or driving it real hard (lots of burn-outs?) the AMC 15 rear axle will hold up well behind the 360. It's a lot stronger than people give it credit for. It's basically the same as the Dana 35 used in Cherokees with the 190 hp 4.0L. A stock 360/4V for 74 only put out a little more power than the 4.0L does. The 360 does, however, have the potential to make a lot more whereas the 4.0L is very near its limit. The AMC 15 has a 7-9/16" ring gear and is comparable to a Ford 8". Plenty of 351 Mustangs run the 8" hard.
The Gremlin six used an AMC 15. I'd still use the Gremlin axle to get rid of the "big nut" driveshaft. The shaft is fine, just a little troublesome even if you know exactly how to set the big nut shaft up. Most take the u-joint apart without loosening the big nut because it has to be torqued to 200 ft/lbs and positioned right. Unless you really need/want the gear ratio it has spring for the Gremlin axle. 73 Gremlin had a 2.73:1 rear axle stock, 3.08 or 3.31 were optional. The "X" model should have one of the optional ratios, so you should be okay there.
The 73 axle code is stamped on the rear of the right rear of the differential on the right (passenger side) near the hole in the housing where the tube is plug welded in. It may be hard to find. F = 3.08, G = 3.31, H = 2.73. The 65 axle ratio is on a tag held on by one of the rear cover bolts, and may be missing. The tag will have the number of pinion/ring gear teeth. Divide the big number by the small to get the ratio. Ratios were the same as Gremlin for the OHV 196. 2.73 stock for man/auto trans unless it had OD -- those used 3.08 or if a Twin-Stick 3.78. If it had a 232 3.31 was stock. Apparently all the 232 models had an auto trans, as no other axle ratios or trannys are listed for the 65 American with 232.
Last edited by farna; 12-11-2010 at 01:07 PM.