Morris Blythman AKA Thurso Berwick was never credited as the writer of The Wee Magic Stane. Morris did write a couple of songs relating to the retrieval of the Stone of Destiny e.g. Superintendent Barratt, tune Barbara Allan and Robin knew that Morris was not the writer. John McEvaoy did indeed go to Canada and is not the Irish singer of similar name.
I still have the original booklet with all the Sangs o' the Stane which has no credits so this may have caused the confusion.