if you want to shoot 120 film
you can take a 3x4 singer / graflex &c roll film holder
that was made for a 3x4 camera and tape it on the back
it might do the trick for you.
i have a graflex 23 taped on the back of my 4x5
that i taped on there and i shoot wide open all the time
never had focus issues ...

have fun !
john