...you need to do some groundwork. Reality doesn't like to give up its secrets all at once.

You see, by Monza 1969, I assumed you meant the Grand Prix (and couldn't see the pictures to confirm). Its September date could well be a good fit with the changeover from "Chronomatic" to "Automatic Chronograph" marked dials.

The Monza 1000 km is a wholly different matter though. It took place on the 25th April in 1969, the same month that the "Project 99" coalition was showing pre-production prototypes of its Chronomatics at the Basel fair. That, if we are to judge by the press release issued in March of that year looked like this:

Note the MH bezel on the Autavia and different text on the dial - the "Chronomatic" is where we would later expect the "Automatic Chronograph" text to be.

If Siffert was able to get his hands on an 1163 at all in time for the Monza 1000 km, it would have been one of these prototypes, which could explain why the watch in the photos looks unusual.

I can't get the photos to display in either IE8 or Firefox 8, which is annoying as I can only see them on my iPhone where the blog software doesn't let me zoom either, but the bezel looks like it might be narrower than an 1163's and where he is adjusting his chin strap, there may well be a crown between the pushers. One of the rare silver dial early Autavias perhaps?

So, I think, rather than busting the idea that Jo Siffert wore a white dialled Chronomatic, all we have here are photos to show that he enjoyed the Autavias before he got to wear the watch that he would later make an icon. That's all.