I have managed to collect a couple vintage film cameras that take 620 film. 620 film is similarly sized to 120 film, but the reels for it are slightly smaller. While you can modify 120 film to fit in these cameras, the easiest way to use them is with a 35mm film mod (similar to the mod that allows you to shoot 35mm in a Holga).
I used this mod to make my Kodak Browning Hawkeye and my Ansco Flex II usable again. Here’s a full tutorial of 35mm in my Ansco Flex II.
1. Tape over the hole used to view which frame you are on (this is for 620 film with paper backing).
Use packing peanuts to center the roll of 35mm film and tape it into place.
Tape the other end of your film to the take-up spool. If your camera doesn’t have a 620 take-up spool, you can obtain one on eBay.
Shoot film. Each camera is different, so you will have to experiment with the number of turns between each frame.
When the film is done, you’ll need a darkroom or light tight changing bag to unload the film in total darkness. Wind the film back into the canister and develop.
Just like shooting film in a Holga, the image will bleed onto the sprocket holes of the film.
Because of the orientation of my Ansco Flex II and Brownie Hawkeye, the shots will be vertical on the film.