I installed Stuffit Deluxe 6.0 on my new g4 733, and while stuffit works fine in 9.2, when I try to open it in Classic the message "stuffit engine not found, please re-install from master disk" (paraphrased) appears.
Are you using the same system folder to start up Classic as you are for your 9.2 boot? It sounds like you are, but I thought I'd ask.
When I run Stuffit Deluxe (version 5) it seems to work okay in Classic, but not if I use it as my file helper from Explorer. The application opens but doesn't open the archive. I made changes to my Helpers in IE to use the latest Fat Carbon verison of Stuffit Expander instead. Now I no longer have to see that ugly retro Stuffit Deluxe toolbar. (I'm sure it's much prettier in version 6.)