Just a report back - thanks Wayne for giving me the tips to make a
successful ProDOS CD. I had to jump through a few hoops, but here's what
worked...
1. Installed Toast 3.5.5 onto 575 - unfortunately, it didn't recognise
my CD burner, but it was still essential to the end result. Toast Deluxe
4.1 crashes, so I'll troubleshoot that later to try and reduce the
number of steps and transfer times below.
2. Connected SCSI drive from IIgs onto Mac and started up - HD didn't
mount anyway, so could leave it on.
3. Ran Toast and chose Device copy, but, with no working CD-RW drive,
chose to save as a disk image on the desktop. Went through pretty
quickly.
4. gzipped the resulting disk image (reduced size from 41 to 17MB) then
transferred via AppleTalk to my PowerBook. Have to troubleshoot the
575's ethernet card to make this faster than 15 minutes :)
5. ungzipped the .iso file and used Disk Utility in OS X to burn to disk.
6. Got CD-ROM drive and HD working on IIgs after much hassle with IDs
and terminators. Renamed HD to avoid conflict.
7. Inserted CD - voile! It turned up on the GS/OS desktop. Hooray!
Thanks Wayne - if I can get Toast 4.1 working I might be able to follow
your instructions more closely :)