Here's a start on the geometry.

http://www.swbmfg.com/rudex.html

Sullivan, DuBro and Great Planes all market a 4-40 size pull-pull rigs that would work well in the Eindecker. I have been gearing up for one on another model and decided to fashion a central bell-crank at the rear of the servo tray and move the bellcrank with the servo. That way I can make servo adjustments while leaving the pull-pull connections tensioned. Ball bearing rod ends eliminate as much of the slop as possible, but the following cable can be relatively loose; as the pulling cable is the only tensioned one. Ideally, the opposite cable should be snug but not tight.