"Machine specific" system software is a myth in its main sense.
In the "old world era" this concept was used only to ensure that the proper set of extensions and control panels were installed on the proper mac model. To avoid that a "powerbook" control panel were installed on a desktop Mac, by example.
The other use was to "enable" a Mac Os System version in to run in a Mac model that was build after such system version.
The more recent version of the system software usually includes the more recent and bug free components. But not always.
I recommend to use The Sawtooth Mac Os 8.6 not only in the "machine specific Models" but in all machines you have with 8.6, because of this. And not recommend in to using Mac Os 9.0.x because is slow, and buggy as hell, even in to its "machine specific" versions, nor as upgrade to a 8.6 system.
Furthermore, my 8.6 install (inside my PM8600 ) contains components of other System versions "as usually".
If you really wish to have a fast, reliable and easy of troubleshooting System, choosing the best components is the way to go, ( despite its different system versions source ) ... and not such "machine specific" nonsense.
I'll attach a picture to compare my 9.2 and 8.6 extensions folders:
... and yes, I was using Quicktime 6 in a 8.6 installation.
because it's the best QT version available for Mac Os 9 (and 8.6)