Okay then.
This motor (probably an early one) threw its water pump. Most of you know why this would've happened - it was the early one with the floating disc that gradually destroyed the inside of the pump housing.
The coolant then exited the car over what must've been a brief period of time, and the motor eventually overheated. The damage seems to have started over cyl 4 ("front" bank, offside) as there is serious discolouration of the cam covers in that area and the spark leads show signs of heat damage. The OS suspension upper bearing has coolant in it too, but that probably came from the expansion tank.
From the look of the left side of the scuttle, the coolant exited the car to the rear under pressure and warped/discoloured the pollen filter cover.
At this point, the engine was overheating badly and unbeknownst to anyone, either the head gasket failed or the front head warped slightly.
Things are a bit hazy here for me, but... The water pump was replaced and the car driven for a further 4-500 miles, with occassional top-ups of coolant. The coolant loss was noted and the car taken to a mechanic who determined that HGF was likely.
Looking at the car today, it's throwing coolant through the exhaust and there are petrol fumes in the header tank. The fumes are bad enough that they're visible when the header is open.
My diagnosis is that the front (left) bank has thrown a gasket near cyl 4. Given the cost of fixing it, the engine is BER and should be replaced (though could be repaired and sold on as long as any head warp is in tolerances).
I'm game. Spaceychick knows how to make tea. Anyone else?