Welll.... got it booted into 9.1 off my iMac test drive, ran the 4.1.9 firmware update so it is X-able, but I'm not quite out of the woods it seems.

The second time i booted it, the display came up with the raster rotated at an odd angle, which i wasnt able to adjust out with the iMac screen control panel, and it is also periodically clicking , leading me to think there is something suss going on on the analogue board. No big issue, as I believe I have a servicable late indigo i can reshell, just a bit of a disappointment is all.