The C330 series uses a rod with distance scales on it. It is supposed to be user-exchangable (if you can find the right version (metres/feet and focal length set)). You might try a scale on the lensboard reading from the front of the camera. The earlier versions worked that way. Just focus the camera on items at infinity, 20 feet, 10 feet, 3 feet, or whatever, and mark the label. Try this link and look at the C220 left side picture. I'm suggesting a linear scale like the exposure compensation scale at the bottom of this picture. http://www.gapatterson.com/grahamp/c220/c220.html
To be honest, I rarely if ever use distance scales. Exposure compensation and parallax indication, sometimes.