You appear to have a 6x6 mask, and I can't tell you how to cipher the framing with that, but if you want to use the full frame to 5 3/4 inches, it's fairly simple to use the existing red window, but I would replace the old red lens with new rubylith before I loaded any film. The numbering sequence for 120 film, using the entire length of the camera's frame, is as follows: Wind the film until you see the number "3" for the first frame. Go past the number "6" to the first dot for the second frame, past number "9" to the second dot for the third frame, past the number "12" to the third dot for the fourth frame, and then to the number 16 for the final frame. Of course, you should also check the bellows for light leaks, and you'll want to put some black tape over the red window except when you're winding up a frame. Keep it out of bright light. I also had to make my own pressure plate to block some light leaks from the back. Good luck, and have fun.

Kobin