Hi!
Any bootable CD will contains a minimal driver and that's why he can boots it off.
Then, because it is a plextor drive, MacOS don't recognise it because of Apple fight to Mac's modifications.
Finally, Apple did give a universal CD driver in MacOS 7.6 (or 7.6.1) because of Mac Clones …
And IIRC, they did the same with 8.6 with a CD/DVD one.
So, if you want to get your Plextor drive working on any MacOS, you will have to use these specific versions of Apple branded drivers.
Or use any Apple hacked drivers.
Or use any thrid party driver (like FWB Toolkit, Intech CD/DVD SpeedTools …)
In my 6100, I replaced the old 2x CD drive by a Pioneer 32x DVD one … and because it is a DVD drive, the universal Apple driver of 7.6 crashes at boot time.
So I delete Apple driver, installed Intech ones and let's go !
Long time ago, this DVD drive was in my 7500 (G3 upgraded) and I had to do the same thing.
The driver itself is not very big and should fit on a floppy. Intech installer is just a piece of software that copies files in the good places so the driver is in a folder close to the installer.
You can find it here :
https://macintoshgarden.org/apps/cddvd-speedtools-60 (after checking, the installation ".sit" itself is less than 1MB)
Finally: I beg all your pardon because I did the same mistake as Teddypotter, I posted my first thread before presenting me (but I present myself some times after)
To Teddypotter, if you want more help on your 8100, you will be better going on 68kmla forum
