Tim,
I looked in the Shop Manuals and I think I know why you are asking the question.
Most of my Shop Manuals are packed-away from moving, but in ones that are on-line I see no mention of the insulator/spacer (but I see it in a few pictures of the manifold assembly).
I think you might be looking in a section where the carburetor is removed and then, later, installed. The insulator/spacer (and, sometimes the gasket) is not specifically mentioned because they were not removed when the carburetor was removed.
What year Shop Manual and what section?
