You should try sticking 120 spools into any camera that is designated 620. Don't force them, but give it a try. While many of them will not fit, many will. Both of my vintage cameras (one of which is my beloved Argoflex E!) are nominally 620 cameras, but I've used 120 in both with no problems.
Respooling is not difficult if you've done it a couple of times. However, something to keep in mind is that the film is taped at the "leader" end. I've found that it's easiest to simply tape the trailer end, and reverse the roll. When you get to the original tape, just peel it off, I peel off the paper, fold it over, and stick it to the film, it's easier than peeling it off the film. The roll will read "Exposed" when you load it into the camera, and look almost like a frest roll when you take it out. Take some masking tape to reseal it, and mark it with an X so you know it's been exposed.
And, as previously mentioned, it's identical with 120 film, except that the spool the film comes on is smaller for 620. You will have no problem getting it onto a 120 reel.
Why, you might be asking, do I know anything about respooling if my (beloved!) Argoflex takes 120-sized spools? Well, I foolishly disregarded advice to try this when I got the camera, and decided that I was going to simply respool. It was a nightmare at first, but then I got pretty good at it. Then, one day, I mistakenly loaded a roll on a 120 spool (or perhaps stuck in a 120 takeup-spool, I don't quite recall). Once I realized it, I was shocked, amazed, and annoyed. Also, I seem to recall reading two other facts somewhere: some cameras will accept a 120 spool on one end but not the other; and Kodak cameras are the likliest to accept only 620 spools, since 620 was their brainchild. Other brands wished to maintain compatibility with established standards.
As for the marking with the X if the film is reverse-spooled: It takes only one roll that's been double-exposed. Also, I believe the leader and trailer end of the paper are different lengths. I always matched them up and placed the end of the film in the same place on both, to make sure that the film would be on frame 1 when the camera said it was. It's hard to say, because it's been a while, and I did it in the dark.