Swampcat,
Don't know about where it was mounted on Art Deco trucks but on Advance Design trucks (47nd-55st) it was mounted into the carburetor inlet. This was not a stock item but was a Chevrolet accessory (AC brand). The mounting location is shown in Advance Design Accessory Installation Manuals.
You are right: some people installed them on the fuel pump outlet in order to keep gas drips off the manifolds.
Tim
