Hi Peter - well you have been busy and yet again you raise another very interesting topic. I love this forum because I am always learning something more about these amazing watches. I can help with some points as follows:

: - Is it the small or the large bezel ring that came first (Mk 1)

Definetly the small ring

: - When was the change from Mk1 to Mk 2. Year and sn.

No idea - this will be very hard to pin down unless we find a big change in serial numbers. For example: Autavia 2446c GMT Mark 1 # 131224 vs Mark 4 #195996.

: - Which compressor-case Autavias used what case (I know that the
: 2446C used both)

: - Are there other differences between Mk 1 and 2. Two case
Something to explore but in my experience the Mark 1 case has an engraved backcase and the Mark 2 has plain/polished backcase. It certainly is the case with the GMT example above.

regards
Paul
www.heuerworld.com