Anybody use a 73 up duster heater box ina 71 duster?

O.k.,this is crazy but I havent found a single person/wrecking yard that can tell me if a heater box from a 73 up duster is a bolt in for a 71.Anybody here swapped one?,I know the heater core part numbers are different but Im looking for some real world answers,thanks for any help!.
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