I couldn't find my instructions to check on that part...but I think I know which one it is...
Here's the trickier part of the cupola's construction...
I was missing a few parts and so I fabricated replacements in styrene...which is why a few of my parts are white instead of gray.
I've thought about using one of these kits as a starting point for earlier cars, but ultimately settled on just scratch building everything for it due to the running gear...
Michael