If you have single piston disc brakes on the front of a '73 they are large bolt pattern. Be aware that the large bolt pattern rear ends came in 2 flavors, 7 1/4" and 8 1/4". There were no A body 8 3/4" rears produced after 1972. '73 340s had 8 1/4" rears, at least the '73 Dart Sport 340 I bought new did.
hence the reason no Mopar part number exists for either side Large Bolt Pattern (5 x 4.5) A-body 8.75 axle. They are all custom Moser or other brand axle, or a cut and resplined c-body axle.