What kind of a G.M.C. 307??? My listings show a V-6 305 with Stromberg 2-barrel carbs, and an L-6 308 that used a variety of Zenith and Stromberg 1-barrel carbs. I have no record of a G.M.C. 307 (listings 1913 - 1974).

Using a 4 barrel through a 4 barrel to 2 barrel adapter is a total waste of time and money. If you want more carburetion, best to buy a larger 2 barrel or change the intake manifold.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop