Update:
Taking both machines apart and rubbing bits together...
The 2MB motherboard works fine and after some grinding noises the second hard drive boots.
Careful examination shows a broken wire on the video cable of the non-booting machine.
The second machine's HDD drops to the shell rather than starting the GUI and the root password is null, so now I'm in as root on the second machine but don't know how to start the GUI or make a bootable floppy. Still, good progress.
Taking both machines apart and rubbing bits together...
The 2MB motherboard works fine and after some grinding noises the second hard drive boots.
Careful examination shows a broken wire on the video cable of the non-booting machine.
The second machine's HDD drops to the shell rather than starting the GUI and the root password is null, so now I'm in as root on the second machine but don't know how to start the GUI or make a bootable floppy. Still, good progress.