Hello George,and all. Desert Dancer, if you are wondering what the Armstrong twins version is like, or others, you might be able to find them at the Public Archives of Nova Scotia on University Ave. in Halifax on your next trip to Nova Scotia. If I am not mistaken I found a few different versions of "If I were a Blackbird" on tape, including the Armstrong twins, (but my memory is short and it has been a while since I have been there and I was not looking for that particular song). The archives have put most, if not all, of Helen's collection on cassette tape and you can visit there and head up to the 3rd floor. From there someone can help you and set you up with a small tape deck and retrieve the tape you need. {There are many more gems there as well.} Barry Smith, at the archives, is the one who is mostly in charge of Helen's collection and he might be the most able to help you.
Good luck with all.
Cheers, Dan