67 and 69 barracuda reverse light housing mounting screws

I'll check the ones on my car ('67).
Have you checked Restoration Specialty Supplies?
Last I looked they had a wide selection of chromed and St st oval head sheet metal and machine threaded screws.
Some are available with smaller heads. They'll be noted in the catalog as #8 with #6 head.
The front grill and headlights use chromed, and IIRC use some of the small headed screws.