Round 2:
IDE time-out to 35
IDE busmastering ENABLED.
Found one called "QUickboot" which was enabled, and disabled it. That just made the PC count to 10 before continuing to boot.
Rest as above.
Still no SSD visible.
I reckon the next step is a device to add 5-second delay on power to the SSD when I can get out to the workshop and my soldering iron. A relay, a few resistors and diodes, and a suitable capacitor all hooked into a Molex Y-cable should do it.