If the holes are below the headlights like those shown on this truck they are most likely off a GMC. These were the factory installed park light on all series of GMC.
https://www.flickr.com/photos/advance-design_parts_co/8130455195/in/set-72157631870734114
If the holes are on top of the fenders like these they were available from several sources including GM as dealer installed accessories.
https://www.flickr.com/photos/advance-design_parts_co/8130556366/in/set-72157631870734114
These could be installed on any truck and would not indicate series.

1950 Chevrolet 3/4-Ton 3600
More pictures on Flickr