Rich,
The notches in the gaskets and in the insulator are needed to allow a vacuum "lead" to a hole in the base of the carburetor (I do not know the correct term for this hole/port).
If you are not using a carburetor gasket, the notch in the insulator is necessary for the vacuum "lead" (the Shop Manuals do not suggest a need for a gasket above or below the insulator).
If you are using a gasket with the notch between the carburetor and the insulator, there is no need for a notch in the insulator (but a notch there is OK).
If you use a gasket between the base of the carburetor and the top of the insulator, that gasket must have the notch orientated in the correct direction (to match the hole in the base of the carburetor).
A carburetor gasket with no notches might be used below the insulator (between the insulator and the intake manifold), but it would also be OK to use a notched gasket (or no gasket) in that location.
Many people simply always use a gasket under the carburetor and often under the insulator (to avoid vacuum leaks).
