I contacted the original designer - Sebastian Jenkins - who said it brought back memories. He thinks he has the original design materials somewhere, never throwing out things like that, but will take some time to unearth them.
The PAL, TTL and memory chips should not be hard to get.
The chips are closely packed, suggesting the board might be four layer.
The NS32xxx chips are closely packed, and generated a lot of heat, needing heatsinks, which would obstruct boards plugging into the Internal bus connector.