Well, I went over to my mum and dad's place this evening and took a look around the attic to find the 286 board... there's sucky news, bad news and good news:
Sucky news: CMOS battery was all furred up and a couple of copper components at the base of the battery had turned green - luckily I think I caught it soon enough and have now removed the battery and cleaned the area with acetone. It doesn't appear as though any damage has occured to the PCB.
Bad news: No docs or manual. I kinda guessed I didn't keep these, but it would have been nice to know the manufacturer, memory capacity and what the various DIL sockets are for.
Good news: Although compact, it's actually a really nice board - it has an AMI BIOS, a socket for an 80287, 4x 30pin simm sockets, 4x 16bit and 2x 8bit ISA slots. There's also a rather large Headland HT12 surface mount chip on the board - not sure what it actually is for, along with 4 empty 41256 and 8 44256 DIL sockets above the simm sockets. Only markings I can find on the board itself are "GW-286" and a part number of "EP40008R32"; there's no manufacturer that I can see.
And here it is:
My collection database and technical wiki:
https://www.target-earth.net