Welcome to the forum Tom.

Now, thanks to Stewart's neat little trick, we can see your photo and provide some more information about the watch.

It's a 3645, as shown in the bottom right of this catalogue from 1962:

The first 3645s pre-date the Carrera, but they continue to be sold alongside Carreras through to the later sixties - we see them in the 1967 catalogue too. However, in or around the Carrera launch in 1964, they adopt the markers and handset of the Carrera rather than the earlier ones we see on your watch, so your watch would appear to pre-date 1964. The catalogue also shows prices, so had you bought it in 1962, you would have paid $65.50. Interestingly, the price hadn't increased at all by 1967 - you would have paid the self-same amount 5 years later too. Or rather, you would have paid the equivalent amount - with the Gübelin markings, the watch would have been purchased in Swiss Francs, as Gübelin is a jeweller in Switzerland. As already mentioned, we have seen several different Heuer models with Gübelin markings on the dial.

Without being able to see a picture, I can't be entirely sure about the movement. Certainly later 3641s and 3645s used the Valjoux 92 and chances are these early ones did too, but some of the earlier Valjoux movements are also a possibility. The good news is that these are well-known movements with far from the worst parts availability for vintage movements.