I like it, nice and simple adaptation to 120 film. You didn't show the back of the camera so we can't answer the question about how to wind the film. Maybe your grandpa wound it by counting winds or maybe he cut out a new red window so he could see the frame numbers. Also it looks like he probably didn't use a take-up spool like a "real" 120 camera does. So you would have to rewind the film back onto the supply spool in a darkroom or changing bag.