Nice find! It's Heuer Ref. 73321T...and its a "post-Carrera" rather than pre. These are from around 1970 and used several of the design elements of the Carrera, but positioned as an economy range at the time.
The case is made from chrome-plated Nickel, with a stainless steel caseback, unlike the all-steel Carrera. Not sure if yours has been polished? The lugs look a little "softer" than I'd expect, but it could just be the photo.
To my eyes, it also looks like a close relative to the Carrera 12 Dato below- a watch that is officially a Carrera, even though it doesn't use the traditional Carrera case (photo by Abel Court)
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