Yes, that's right, toothbrush, the engine looks like it has had a rocker cover gasket leak (seems to be a recurring fault with this engine after the inlet manifold) and there are areas (especially on the inlet side) that are covered in oil. I tried Cilit Bang but didn't do much so resorted to petrol and a toothbrush. So, I got most of the engine clean but there is a layer of grime on the surface that will need wire brushing away. Got to leave some jobs for another day.
Also did a quick measure of the engine and I will have to do something about the rear of the engine. There is a casting that connects to the coolant system and acts as a mount for the coil pack which sticks out from the rear of the head. This will mean moving the engine forward 100+mm which I do not want to do. I have seen slimline mods that move the radiator inlet to the inlet side but currently haven't found where to source them from.