I'm back to Stuffit and OS9. Once you make an SEA, Stuffit can
split it up for you into whatever size segments are convenient. If
the final user has OS9/Classic, double-clicking on the first segment
will automagically join all segments together and un-stuff the result.
That's Stuffit Standard or Deluxe. Not the freebies that accompany
the Mac OS. You need to buy a copy. The final user doesn't.
It's worth pointing out that if you're familiar with the command line (os x) you can just use a zip file and split it.
Use the "make archive" command in the finder followed by:
split -b xm
where x is the size in megabytes you want each chunk to be.
Then on the other end they can use:
cat file.1 file.2 file.3 > output.zip
and the zip should be fine.