[dp_burke]

This old thread on RAFCommands suggests it is Anson NK607

http://www.rafcommands.com/cgi-bin/d...rum=DCForumID6

And there are other threads also:

http://www.rafcommands.com/cgi-bin/d...D6&archive=yes

http://www.rafcommands.com/cgi-bin/d...ic&archive=yes

And also here:
http://www.rafweb.org/Help_Wanted.htm
I hope this helps, I found these by searching for Chapman and Anson etc in google.