I've had fairly good luck lurking on here for old 220 film. Outdated E-6 can have quite a bit of color shift, but I haven't run into any yet that couldn't be handled in digital postprocessing---there seems no longer to be any realistic analog postprocessing for E-6, alas. But if you're targeting projection, color shift obviously would be a concern.
I looked at the user manual for the Yashica 24 and it doesn't say that you can use 120 film in it, but a number of web pages claim you can; maybe it's an undocumented feature? Might be worth a try in any case.