I have a bunch of mid-80s touring bikes. They all still wear 27" wheels. It's got little to do with "originality" but more to do with "qualilty" and I don't want to futz with canti pads at goofy angles.
While I have seen some 27- 700C conversions that look great and natural, I've seen a lot where the pad angle is much more down than in.
You may wish to see the blog for forum member [MENTION=178668]The Thin Man[/MENTION] and his really nice redoing of a Kodiak:
1985 Raleigh Kodiak :: Spring Cleaning | The Simplicity of Vintage Cycles