Hello,
I just had the same problem today and I fixed it by unstuffing BootX with a more recent version of stuffit expander.
I wanted to install YDL on a mac OS 8 system. I couldn't unstuff it.
I have another mac with OS X and stuffit expander 8.0.2. So I mounted the Disc 1 ISO and unstuffed the BootX on my OS X system.
Then I used a Zip100 to bring the unstuff app to my older mac.
there you go it worked.
I hope this help
P.