Lonnie's last sentence is important. Some of the after-market insulators do not have the "slot" in them for the vacuum port on the base of the carburetor. A gasket with the vacuum port/hole cut-out is needed or the carburetor will not work properly.

Of course, someone with Denny's skills and equipment could machine the slot into a replacement insulator.

Here are insulators that have the correct slots in them.

Here are some more with the slots.