More: Found another way to make a universal install (theoretically):
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All retail OS 9 Install CDs, and most OEM ones (the ones labelled Software Install, not the ones named Software Restore), have the ability to perform a Universal (boot any Mac) install of OS 9. Perform a universal install of OS 9.0.4, update it with universal installs of the needed updates, and it should work fine when transferred to the other machine, provided that the final version is one supported by that machine.
QUOTE
To do a universal install -
1) Boot the machine to the CD if necessary, then run the installer. Step through the pages in the installer (choosing the correct destination volume in the process) until you get to the "Install Software" page, the page with the "Start" button on it. Don't click that button.
2) Click the "Customize" button at the bottom left of the page.
3) On the new page, click the pulldown menu to the right of "Mac OS 9.x", and select "Customized Installation..." from the list offered.
4) On the next new page, at the top is another pulldown menu labelled "Selection:" - click that menu and select "Universal Installation".
5) OK that page, then click the "Start" button.
These instructions may apply to the OS 9.1 download update, do apply to the OS 9.2.1 download update, but do not apply to the OS 9.2.2 download update.
Which Macs take what version of 8/9:
http://support.apple.com/kb/HT1835