The 7042276 is not the same as the 7042270 Ram Air carburetor. The 270 was used on the Pontiac 455 "HO" engines, which had round port high flow cylinder heads, and Ram Air.
The 7042276 was used on the base engine(s), not the High Output 455.
The Ram Air carb is extremely rare and valuable, the 276 carb is just a standand unit, probably worth about $25-75 as a core, depending on condition......Cliff