This thread was basically a response to a question about the G.M.C. 270.

If you check this link:

http://www.thecarburetorshop.com/TruckkitsG.htm#TkitGMC

You will find G.M.C. used Zenith 28AV11, 28AV12, 28BV11, 28BV12.

And Zenith made the 28AV12 WITH DIFFERENT INTERNAL VENTURI SIZES for engines from 245 CID to 525 CID.

To determine the airflow, one MUST do more research than just the carburetor type.

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