The photos of Siffert seem to show him wearing an Autavia, reference 1163T, in the earliest version (with the word "Chronomatic" above the Heuer logo at the top of the dial and the word "Autavia" at the bottom), like this one.

There are those collectors who say this is the only real "Siffert Autavia".

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Based on common / popular usage, most collectors would call any of the automatic Autavias, reference 1163T, a "Siffert". So these two also become "Sifferts" under this usage.

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Finally, there are those who would call any of the Autavias with the white dial / black registers and this case style a "Siffert". Under this approach, this one also becomes a Siffert.

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This discussion / debate can be repeated for the McQueen Monacos.

So what is a "Siffert"?? It depends who you ask.

What are the "Sifferts" worth?? A lot, compared with any of the equivalent black-dialed Autavias.

Jeff