Question on drivers side exhaust manifold gasket

[340wedge]

A friend recently gave me a sheet metal exhaust manifold gasket for a 318. Does anyone know the difference between the 318 and 340 gasket? I saw something a long time ago on how it can be modified to work for the 340 but I am not sure what it was. Thank you.

 

[Professor Fate]

Early or late 340 manifolds? They're different.
So first off, see if it clears the manifold.
Then lay it on a 340 head, you'll see what has to be removed. If I remember correctly, early 340 heads (X, J) have ports that will outsize those gaskets. Later 340/360 heads you may be safe with, and may not even require modifying.

 

[413]

318: The ports are too small and the center has a divider on the 340 gasket. Not one open hole like you have.