Well, it turned out the seller had a G4 board in stock, and although he wanted an extra $90 I went for it.
It also turns out it's a 550, so I might be tempted to give Leopard a whirl, give that I have a Carbon Copy Cloner USB drive to fall back on and that I've proven to boot.

I now have a G3 400, 450 or 500 to spare if anybody needs them, although I'll probably keep the 500 just in case.
Cheers
Hugh
It also turns out it's a 550, so I might be tempted to give Leopard a whirl, give that I have a Carbon Copy Cloner USB drive to fall back on and that I've proven to boot.

I now have a G3 400, 450 or 500 to spare if anybody needs them, although I'll probably keep the 500 just in case.
Cheers
Hugh