It was an aftermarket "fix" (Baldwin-Washington part number 20-2989) which (opinion) would make the warpage worse. Carter did not use it.

For sealing purposes, the thinnest gasket is virtually always the best.

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