If you want to take pictures of a C8A HUA, try to contact Nick Bullock. He owns the ex-Bart Vanderveen HUA which was later restored by Ian McCallum:
http://www.mapleleafup.net/forums/showthread.php?t=5524
John Corden and Marty Morren have HUMs. All of them are on this forum.
There are a couple of C8s kicking about in the UK, too.
Looking forward to your book on C8 & C8A’s.
Hope this helps