I stand corrected---my very own 6.5x9 Avus has an Ibsor shutter, not a Compur as I thought. I couldn't get the lens elements off without more force than I wanted to apply, but from educated guessing about where the threads are, I think it's probably the standard dimensions as given on the French site: 29.5mm diameter, both front and rear. If it varies from that size it can't be by much.

There's a photo at http://www.flickr.com/photos/rebollo_fr/4826112985/ of a 6.5x9 Bergheil mounting the 20cm Tele-Dynar; it's in a rimset Compur shutter with speeds to 1/200, for what that's worth.

-NT