73 duster rear end

Most 73 225s had 7¼" rear ends. These units are as common as dirt. What is not common is finding one with Sure Grip. Mopar made them, but I haven't seen one personally. The 7¼ had smaller diameter axle tubes than the 8¼ and 8.75. If you decide to go with an axle with a larger diameter tube, be sure to grab the shock plates and clips (u-bolts), too.

Did your car come with disk brakes from the factory? If so, the wheel bolt circle pattern on the axle is 4½". Otherwise, with drum front brakes it had a 4" bolt circle pattern.

Any A-body is a potential donor. Rear gear ratios vary depending usually on engine and transmission. A very common 7¼" rear for 1973 225/904 combinations is 2.76:1. Other factory installed ratios used in 1973 were: 3.23:1, 3.55:1. The best way to check the axle gear ratio is to find a bronze tag attached to the rear cover. The tag will be stamped with the installed ratio. These things had a tendency to get lost, so you may not have one. The other place to check is on the build sheet (D51, D53, D56 respectively).

I've replaced a wheel bearing in a 7¼. I used a Dremel tool with a cut-off wheel rather than a cape chisel to get the old bearing off. Other than that it was straight forward and greasy. Good luck.