Does anyone know if the trunk pan and the rear floor pan from a 74 Duster are exact replacements as the same two items in a 74 Dart Sport?

I will hazard a guess that they are. I think the only differences are the rear tail panel (where the brake lights go) and the front clip (fenders, hood, grille, bumper).

You are in luck ..Same!!

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Michael Glass. Mopar stuff and some rusty Mopar stuff!
1965 Dodge Dart with 66 Valiant front clip. Other stuff...

The 1973-1976 Duster/Dart sport bodies are the same...the only real cosmetic changes are the rear panel (tail light bucket difference)...and that the 1975-1976 front floor pans have a 'bump' under the driver's seat for the catalytic convertor, front clips are interchangeable, and the stickers are different...but you can take floor pans from one and put in the other / vice versa...

-D.Idiot