Edlebrock 9266 manifold gasket won't fit stock LA 340 intake

This is why pictures are helpful.... Based on your first post, I thought you were having an issue with an intake manifold gasket and couldn't understand what issue you had. What's pictured is a carburetor base gasket and as already mentioned by others, you have a spread bore manifold and a square bore gasket. The AVS2 is a square bore carb so you will either need an adaptor to run that carb on this intake, or a different intake.