Tomorrow I'm 3D printing some "end caps" I modeled in Google SketchUp. They will snap on to the ends of 120 roll film and then (hopefully) slide into the cameras - I'm doing a set for a 122 format camera and a set for 130 format. To convert the film gate I just cut some aluminum flashing with a box cutter, sanded it smooth, painted it with cheap flat black spray paint. I'll glue the strips into place with some superglue type stuff.
If it works, I'll do up a little tutorial. If it doesn't I'll hang my head in shame and drift away :-)
Any comments/suggestions etc are more than welcome!