I would use a gasket between the new insulator and the manifold, as well as a gasket between the carburetor and the new insulator.
The aftermarket insulator is made of a different material than the original one. It appears to be hard plastic.
But I also would recommend the two gaskets for a used original insulator due to slight deterioration common on this 60 year old part made of who knows what.
Carl


1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission