It was also a good excuse to get some hot air soldering practice. I think I'm starting to get the hang of it.
I didn't have a PC available, so I used the Macintosh-based firmware updater. For that to work, I had to install Mac OS 9.1 (neither 9.0 or 7.6 would cut it). Digikey was out of the M25P10-AV, so I picked up an the pin-compatible W25X20CLSNIG.
Once the ROM was updated, the card works like a charm.
I wanted to take my 9600s dual-head, and I managed to pick up a batch of 5 Radeon 7000s on eBay for $29 (total). They're a slightly different card from 'Hightech Information Systems' , but use the same 8-SOIC flash. I figure I'll swap out the flash chip, reflash them and see how it goes. Assuming this works, I'll have a couple extra.
Interestingly, this card doesn't have the 1x1 monitor bug that the card I saw on the previous card (pictured earlier in the thread) when used under Mac OS 9. In that case, an additional 1x1 monitor shows up in the Monitors control panel, but nothing else seems to be affected. I ought to try booting 7.6 with the new card to see if the problem occurs there.