Hi Murray,
    I just noticed this old thread.
My ancestors came from Rum to Cape Breton in the early 1800's.
My people always spelled it Rum and pronounced it "Ro-om."
Now it seems to be spelled Rhum and often pronounced as "Rum."
I think that the Englishman who built a castle there after the clearance tried to spell the Gaelic sound with an English phonic.
    I have recently recieved a package in the mail from a person   there. The return address says "Isle of Rum."
                      Slainte,
                           Sandy