So,

second test was also perfect. Booted from a firewire drive, using an old RAGE128 Pro mounted vertically in the AGP slot. Ran happily for a few minutes.
Not sure if I mentioned it anywhere or not, but the drive module I bought on eBay comes with the rest of the spare parts kit. My current board is a single 1GHz. The new one is a 1.33.

I need a case for this damn thing.