The compact flash to IDE adapter arrived, and it's the right one! Hooray! This plugs directly into the motherboard without need for any IDE cables and gets power from a floppy drive power connector.
I was worried it would be too slow running from compact flash but it's not noticeable. The POST is the slowest part of the boot, and once it's complete it only takes about 1-2 seconds to bring up the menu.
The other advantage of this is it's easy to swap out CF cards to try different installations.
I've also have some car speakers working, I had to bend these small connectors to fit the blades, but it's better than the clothes peg I had before and also means I don't have to solder the wire directly. They are not real world ready as the wires are too thin and any weight would break the wire off. The magnets are holding them onto the side of the old server in this pic.
There is still some problems with the sound. The headphone socket is way to loud, and the line-out socket is too quiet. I'll have to find a simple amp to boost the volume, and that will also give me a volume knob to mount outside of the machine.