JayCee - There should be numbers stamped into the side of the generator case that we can use to decode what it is. You may have to do some cleaning to allow for viewing/picture taking.
According to a little research through some resource documents, your '54 GMC would have been originally equipped with one of 3 different generators. All are 6 Volt. The original units will have one of these 3 numbers stamped on the generator case:
1100018 = 45 amp 6 volt (Delco Remy offered an "18-U" Rebuilt starter as replacements for this unit)*
1105009 = 40 amp 6 volt (Low cut-in rpm)
1106757 = 55 amp 6 volt
* This unit also listed as standard equipment for Chevrolet trucks of the same year.
Resource info taken from a 1954 AEA Original Equipment Parts Catalog and both GMC and Chevy Master Parts Books
