I just got it to install and run. Here's what *I* did. You may not have to go quite this far back but ...it's worth it to know , IMO, that it can work right this way. PS EDIT: It STILL gives me "Cannot find the plug-in Play; make sure it is installed and enabled in the plug-in manager." so it's still not particularly useable for me, but at least it didn't crash on launch this time. SO IDK if this will do you any good or not.
I have multiple HDs so I did a computer-wide search for all references to Notion, deleted them and emptied the trash.
Then, going to Older versions and starting back in 6.0, I reinstalled each consecutively, telling Mac OS to keep both. I checked each along the way, then quit it, and downloaded and installed the next, keeping the previous each time. It was a shock to see that 6.7 now works too.
Now if I could get it to figure out where the sounds for it are and work with SO pro.. :)