I am by far not the MP54 expert but……
P54 coaches could be hauled by steam locos because they were not powered.
MP54 were powered. I have not seen an unpowered car of any kind in a MP54 train. If a baggage was needed a MP54 type car was added. See photo.
(photo © Bill Lane. Reproduced with permission,)
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Modeling the Mighty Pennsy, PRSL & Reading in 1957 in S Scale since 1987
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