StuffIt sometimes comes with OS discs, but I don't remember it coming with OSes as old as 7, more like 9. Any version up to 5.5 works on 68ks, though I'm not sure about 7.0 as I always use 7.5.5 as a minimum. There is an issue with using very old versions though, they changed the format of the archives at some point and I think the two are incompatible, but which you need will depend on which the archive you are trying to open is. I would try with 5 or 5.5 first. I got my copy of 5.5 off some OS 9 discs.