I've tackled a few of these economy models recently. Most of them have rung a few bells with me, and I have been able to go to the relevant catalogue and link the relevant pictures pretty quickly.

With this one though, the case wasn't immediately familiar from a Heuer perspective.

Valjoux produced the 773x family in huge numbers and they were used by lots of well-known and less well-known watch manufacturers and brands, but that signed bridge is a bit of a warning sign too. In Heuers, I have only seen them signed like this:

or left unsigned in some of the watches they appeared to be producing from parts bins around the end of the 70s/start of the 80s.

But I thought it was worth having a look through the catalogues anyway. Valjoux introduced the 7733 in 1969 but Heuer didn't adopt them immediately, only starting to use them end of 1970/start of 71 so that gives us a good start point at which to look. Production ended in circa 1978 so we have an end point too, though stocks lasted beyond that, so we are trying to find this model over about a decade in total.

I didn't find anything in there with a similar case. But I said earlier that the case wasn't immediately familiar from a Heuer perspective. It did remind me somewhat of another watch, though, so I did a bit of digging and found this:

It can be hard to be definitive around the late 70s, but we do have pretty good coverage of Heuer catalogues from then. We know of some genuine Heuers that never appeared in catalogues too (hello first generation Skipper), but with this one I strongly suspect it started life as a Kelek and gained some Heuer markings at some point in its life. Though Kelek and Heuer were pretty close to each other in La Chaux-de-Fonds so there might have been some case sharing going on. Were, because Breitling bought Kelek in 1997 and I don't think they are a going concern any more.

Sorry if that's not what you wanted to hear, but maybe someone else has some more info.