Welcome to the forum Ed.

And that would make a fine first vintage Heuer... But then, as a Carrera collector, I might be a bit biased.

Rich Crosthwaite's price guide is robust and well-researched:

http://www.heuerpriceguide.com/

I think in places it's a bit toppy, but you might have to stretch a bit more than the suggested for a genuinely NOS 73453.

Happy to run an eye over photos too, if that's of help, either here or via carrera_table_mm@btinternet.com if you'd like to keep it under the radar a bit more.