67 GMC CST Cab lights factory?

[TonyM]

My 1967 GMC CST has U01 Marker Lamps on the SPID and the 'aftermarket' or 'dealer installed' chrome 77 yankee lights. My cab doesn't have any raised bumps for the cab lights; however, I don't think that they made those cabs in '67. As you know, the '67s didn't come with any side marker lamps/refective lenses, so what else would the U01 Marker lamps on the SPID be referring to?
I did some research but haven't come up with a good answer. Were these installed by the factory because they are on the SPID or am I missing something? Thanks for the help!