This is a nice vehicle.. 10 years back, I was in regular email contact with the then owner and restorer of this truck ( south coast UK area) ... He sadly was forced to sell it due to health problems.
http://hmvf.co.uk/forumvb/showthread.php?t=9913
Jim, you can see the speaking tube setup on this Humber... the whole concept was sent over for the Canadians to build.