If you have no special reason to use the images from the dev CDs, here are some collected:
http://macintoshgarden.org/apps/macinto ... -mac-os-81The Macintosh Anthology also covers localised MacOS8 versions in Dutch.
The .img files from DVD may be moved onto a say 2GB Mac volume via the Unix folder to run the OS installer.
You may also copy a MacOS .img to a place on your MBP and add the .img to the SheepShaver volumes list.
I feel that mounting .img from within Basilisk II with DiskCopy was more successful, but my memory may be incorrect.