I am no expert on the 73463, Siffert or otherwise, but you have certainly picked a hard to find reference,(in watch terms that means $$$$$)with which to start.
Personally, were I still a student with a hankering for a Heuer, I would go for the best Autavia Viceroy or Carrera 1153 I could find and keep the substantial change for the bar.
However if you are truly set on the 73463 Siffert it could be a little while before another comes along.
tony