Jeff and Chuck are spot on with their observations.

It does seem to be a mix of Daytona, Montreal and Verona.

Must be a Daytomontrona then?

I think the cal 12 is the right movement for this watch as the first reference to it in the catalogues turns up in 1977, well after the change to cal 12. Heuer, of course stuck with the 110 movement reference on the case, just to confuse us.

I have owned 2 Daytonas, both blue dial. the first had a solid blue dial, the second a graduated blue dial. Heuer show both in their catalogues, but don't differentiate with a model number, they're both stamped R 110.203B. I have had my hands on a smoke coloured dial Daytona (in John Lloyd's shop in Clerkenwell, London) about 4 years ago. He wanted £650 for it, sadly I didn't have the money at the time because it was in almost new condition and had the racing box and all papers. (Daytonas were fetching about $500 on ebay then)
Anyway I think that Graduated Smoke (Fume) Daytona was absolutely correct and probably had a case ref 110.203F.

Maybe it could be added to the case ref list with a note "thought to exist"