Re spooling 120 onto a 620 spool is super simple and only takes a scant few minutes and requires two (2) 620 spools. In total darkness, wind the film onto the first 620 spool taking care to keep it tight, then transfer onto the second spool, and while keeping the film and backing paper tight, here's the hardest part, make sure the free end of the film stays under the backing paper. If you end up with a bump in the roll you messed up, but by spooling onto a 620 spool first this rarely happens. If you transfer onto a spare 120 first you are almost guaranteed of getting a bump in the roll. After you've done this a few times it becomes second nature.