thank you dddd for the excellent pictures of your mount.
i suspect that some of the differences you mention may not be only between Clubman and Bergmeister as they may be differences through time as well.
Steyr also made a Reynolds 531 model bike for Sears in the late sixties. iirc it came with an SR Silstar chainset and had a flambouyant chartreuse paint scheme. huge clearances and a long wheelbase.
the missing headplate on the present steed would have been of stamped aluminum sheet with black writing.