reo_guy, it's in my '54 book too, listed for models 100 on up. It lists 12V headlight bulbs like they used before sealed beams so it seems this might have been an option as early as '41.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.