In '54 the supply line was moved to the sending unit. Earlier trucks had the supply line on the bottom. Sounds like you have the '54 and later type.

I have never heard of a vented sending unit. As far as I know all these trucks are vented through the cap, outside the cab. I wouldn't want a vented sending unit in the cab.

"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.