Okay, I have Basilisk II up and running: MacIIci (68030) or Quadra 900 (69040), both booting into 7.5.5.

I can mount a Unix volume for transferring files to MacOS 10.11.6 on my MacBook Pro.

Now, I want to install 8.1 but I am sort of stuck. I do have a couple of Developer CDs:
- August 1997 (System 8.0)
- February 1998 (System 8.1)

I can make a .dmg file but I can't seem to mount it in Basilisk. Perhaps someone has some guide on how to do this?
I'd be happy to share my experience.

You need to make a CDR file, not a DMG file. When creating the image, select the CD/DVD Master disk type.

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-81
The 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.

I did all my installs on BII from a 7.5.5 starter that I created the traditional way -- all the rest were images loaded by Disk Copy inside BII along with a blank volume image to install onto. Remember that you didn't have to boot from the OS version you were installing back then.

Guys, have you had any luck to run Mac OS 8 in BII without crashing? I crashed a lot. Thus, I stayed in 7.5

_________________
There is an App for that!
https://github.com/rickyzhang82

I can run 8.1 in BasiliskII in OSX (now macOS 10.13). Main issue is not crashes but the button in window scroll bars not giving feedback (it stays in one place during scrolling). I do not use it anymore since I installed 8.1 in SheepShaver. I tried it just now to see if it still works. I don't think 8.1 has much advantage over 7.5.5. Possibly 7.6.1 would be better, it was the most stable version at the time.

I've been running 8.1 in BII since around 2006 on Windows and OS X hosts. Just make sure you're using the Quadra ROM and have a sane extension set.