Allis Chalmers used dual single-barrel updraft carbs on their model L tractor from 1933 to 1942. This was on an 844 CID inline 6.
Not GM, but closest I have found so far.
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
