Yes, that’s the vent and ashtray. I don’t think that they would have been ordered as extras, my uncle was also a non-smoker. I did have the chassis build sheets for those Mercurys but they were discarded a few years ago when I had a massive clear out.
I was thinking of the double-pole electrical thingy myjig for the Pet Regs, so the double skinned cab was a red herring. Senior moment. 