According to the online GM parts wiki it is a GMC set for 100-22, 150-22 etc. The 22 means 228 engine which means '53 or older which means 6V.

Dave, you are right about these gauges being used later. I saw a '60 something school bus with them. Definitely 12V on those.

"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.