To make the 120 spool fit the small metal tabs better cut short pieces of plastic drinking straws for bushings on the 120 spool. About 1/8 inch long to 1/2 depending on the film spool you have. I just poke the straw in and cut it off with scissors.

It doesn't help the fact that the take up side is way too narrow, but it keeps the supply side from slipping into the slot and getting stuck.