Mario,
I am new to Heuer and to the Siffert, so I didn't reply as I didn't want to provide incorrect information. But now you have taunted me into replying and potentially revealing to the entire community that I don't know diddly.
I would recommend that you peruse these two pages - scroll down to the "Automatic Autavias" sections to see the differences between executions. Or do a search for Siffert on each page.
http://www.onthedash.com/Guide/Master_Reference.php4
http://www.onthedash.com/priceguide.shtml

So far, I'm safe. Here's where I may go astray - the 1163 (automatic) Autavias which have the white dial with black subdials, blue chrono second hand and blue accents are referred to as "Sifferts". Some even refer to the manual-wind Autavias with the same coloration as Sifferts, but generally they say Siffert colors.

There were several 1163 Sifferts sold from internet postings in the past 2-3 months. I believe the lowest price was around $6500 and the highest around $8800. I do not believe any Chronomatics have been posted for sale in that same timeframe (Sifferts or not) except for 1. The one I have seen is on Nic Green's new site and no price is listed (smart, I believe). He also has a Caliber 12 version listed at £8000 which should serve to help you feel good about buying that watch if it is still available. If not, Nic's got one for you!

I hope this helps.
Mike

: Thank you George, appreciate the response as no one else seems to
: know about it. I'm trying to buy this watch not sell it so just
: wanted to know a fair value for it. So even though this model is
: the calibre 12 and not the original Chronomatic that Siffert
: wore it would still command in the +/-US$10,000? Do you know if
: Siffert also wore this same model? They call it Siffert but I
: thought the Siffert was only the Chronomatic.
: Thank you for your time and expertise, truly appreciate it.
: Regards,
: Mario