angle finder for ground glass focusing?
i'm making a kind of weird camera and what i'd like to do is mount a long loupe or an angle finder in such a way that i'll be able to focus off a ground glass from outside the camera. ideally the glass will be mounted inside the camera and the end of the viewing device will protrude from the body. looking at loupes, it seems as if there really aren't any longer than the horseman, which is just too expensive. but i can find a ton of angle finders for various cameras all over for not much more than $30.
my question is whether this will work. if i just butt the end of the finder up against the ground glass, is this enough, or is there some sort of special coupling that needs to take place.