Hello, what you've been offered is most probably the Valjoux 7750-powered so-called "Non-Pasadena", with the great moniker that Chuck Maddox gave it.
If so, it is indeed an original Heuer from the same period (late 1970's) as the Pasadena and most of its features are indeed identical, including its movement. It may be a 'date' instead of a 'day-date' as the Pasadena is.
The proper bracelet found on most of these, based on my 'literature' knowledge, is indeed the flat link one also to be mounted on the 510.50x Lemania 5100 family. Its clasp indeed is unsigned.
Hope this can help, otherwise pls. post some photos.
Cheers.
Fabrizio