You need another serviceable rangefinder. The lower mirror is actually a prism. See:
http://www.graflex.org/helpboard/viewtopic.php?t=6319 Copy the pictures to your computer for future use as the image hosting site is no longer free and I am not willing to pay for image hosting.
Both makes in good working order are very good and as precise as their calibration. Hugo Meyer were made for one focal length only and have enough adjustment to compensate for production variations of lens. I have an Anniversary Speed with a HMRF marked for 127mm and it just adjust for a 135mm Zenar with an infinity focus point of roughly133mm from the film plane.
Kalart rangefinders are adjustable for focal lengths from 101mm to 162mm. See:
http://www.cameraeccentric.com/html/info/kalart_1.html