Help with BBC valve covers and heater housing

[madden]

hi
can anyone help me and tell me how to tell if the following parts are original oem GM
1) what markings or ways can you tell if chrome and orange painted BBC valve covers are original gm parts? what are the tell tale signs?
2) what markings or ways can you tell if a BBC heater blower motor housing (the large one that goes on the passenger firewall on the inside the engine comparment is oem?

i have several sets of bbc valve covers im trying to tell if oem or aftermarket?
and have a nos condition bbc heater core box im trying to figure out if its oem
thank you so much
happy new year to all
chris