Jeff; Nice to finally meet you, your wife and mellow pup!
Do you currently have the CMC front directional base, or are you trying to upgrade to something else? (Or do you have no base at all?).
The CMC base is a Signal Stat part, mostly used on trucks, but I haven't found a P/N in a quick search yet. That base fits the original (glass or plastic) 356 lamp lens and is the same OD as the 356 part so it fits the shape of the horn grill to a T.
If you have the shallow white lens you may have to use a 1/8" spacer gasket to move the lens out to clear the bulb, but the trim collar will still fit.
As an aside, I have attached a PDF with all of the dimensions for locating your steering column properly. They came from measurements taken on Pearl, along with input from Al Merklin.