My three Ikontas:
They are pretty flat when folded up. The widest one i 6x9, and the other two are 6x6.
Sprocket image using the Zeiss Ikon Nettar 517/2 6x9 camera:
Sprocket image using the Zeiss Ikon Super Ikonta 531/16 6x6 camera:
The quick and dirty way to do it is to use some packing pieces to center the 35 mm canister in the camera, but how many turns to wind the film on is just a guess and varies as you wind the film on. You might experience light leaks.
The smarter way requires a totally dark room: tape used 120 backing paper to a table, tape one end of an approx. 82 cm length of a 35mm film (or half the length of a normal 36 exp. film without the leader) to one end of the backing paper and roll the backing paper with film onto a 120 spool. Then it operates just like a normal 120 film.
The two Nettars cost me approx. 40-45 USD each, whereas the rangefinder Super Ikonta with faster lens cost me approx. 150 USD