Correct paint color for a 1970 Dart 8 3/4 axle assembly
Bare metal for the housing. Red oxide for the diff. I have several original housing here with OEM markings everyone is solid rust no sign of paint at all.
I also have differentials carriers with markings they are a red oxide. Your carrier should be 489 for 1970 not 741.
Not much of anything under these cars have paint on them . Lower control arms were dipped partially in a cosmoline coating. Even K-members seamed to be bare metal. Could be why most everything under these cars rusted.