This came up over on the 'I just picked up..." thread. The question was directed at Francois, but I'm going to butt in and give a brief overview of what I have done and the lessons learned.
I have an Agfa PD-16 Clipper. I wanted to use 120 film, so I did some reading and found that the flange on 120 is about the same diameter as on 616. Check... it will fit in the camera. The spool is NOT the same length, nor is the inner post the same diameter, so some tinkering will need to be done. I downloaded a file from ThingVerse to make the spacers for the ends of the 120 spool so it will be long enough. Bad idea. They were too big and I spent more time sanding and reshaping them than I should have. Get a couple of drywall anchors and stick them in the holes in the ends of your 120 spool and call it good. Now next time you develop a roll of 120, don't cut it. Tape it back onto its backing paper and use it to figure out the number of turns of the takeup crank for each exposure. The 120 numbers will show through the red window of the camera, but they are not far enough apart, so tape the window and ignore it. With the back open, get your practice film loaded and count the number of turns past the "Start" arrow to get the end of the film lined up with the mask (actually give it a couple of cm past the mask). That's shot 1. Now mark the paper at the end of the mask nearest the supply spool and wind on until it is a few mm past the other end of the mask, counting the number of turns of the crank. That's shot 2. Continue on like this until you reach the end of the film. It should be about 6 shots. Now you just have to keep track of what shot you are on and make a table telling you how many turns for the next shot. I have misplaced the electronic copy of mine, but it will be different than yours since the Clipper shoots squares and not 6x12's.
There is a pic of the spool extenders here, but like I said, go low tech and save yourself the headache.
http://jamesharrphoto.blogspot.com/2013/12/clipper.html
