Anyone have a link to a design for an incidence meter?

To the best of my knowledge there are but two design in production, the older beam type with a jeweled needle and level made by "robart". The other design I have not used my self but is a laser set up a beam that I think is self leveling, It is available from Tower hobbies.

You said "design"... Do you want to build one yourself?

My favorite, reliable for many years, is the Robart model. Without bashing the particular company, I have to say that I hate the new laser version of this thing, sold by another company. Robart's is a lot more useful to me.
http://www.robart.com/Tools.aspx

Buy two, and you'll find that alignment issues cease to exist.