Now that everything’s been made safe and transported home I could take it all apart, so here is a selection of pics from that:

The original design of the mac was very clean and rather cunning – the
‘analog’ board (that held all the electronics for the monitor) forms
one side of the machine, with the ‘digital’ board forming the bottom.
So although I won’t be putting my smaller Mini-ITX motherboard there, I
will be getting some stiff plastic in to replace them, to give
structural strength and allow me to mount things on them.

Happily there was a big warning sign attached to the side of the analog
board, which will make an excellent template for the replacement:

Right now the lounge is full of bits of mac and bits of PC kit, and I’m
having a bit of a think about how to put it all back together again!