if your rear brake bolt is long enough, try to find one with a fixed center brake bolt mount. they look so much classier on vintage bikes than those using the seatstays. but finding an old blackburn like that is getting more and more difficult. if you do find one, they're well worth $50ish.
i don't understand why these are not more common anymore. the newer, cheaper racks will allow a center bolt attachment, but it's usually a separate purchase for the bracket, and they don't look nearly as 'clean' as the old blackburns with the fixed center mount.
also, remember that if you find an ugly one, you can polish it up like any aluminum component using sandpaper and mother's.