I believe the gasket for the manifold, I personally would not think it would be worth the work//massive reversion issues==no throttle response/no mid range... better off finding a better carb..... or port match/polish a post 66 4bl 273 intake..
As long as the port in the manifold is the same size or bigger than the port in the head it’s fine. When the intake manifold port is smaller than the port in the head I whe it’s very bad.
