1973 Parts Book shows the plug as 1392 371 (supersedes to 2129 351) and the gasket as 2070 122. Application is 7 1/4" and 9 1/4" axles. As you can see those part numbers are long in the tooth. '62 parts book shows the later number (that's weird) for the 7 1/4" axle.
According to our local dealer, the plugs were bought out in bulk from Chrysler and now show $38 each, and the gaskets are available on the parts locator, and show a dealer cost of $.25 - no idea what each dealer will be asking for them.
SC