If you don't have a pressure washer, squirt some oven cleaner on it, avoiding directly spraying on non metallic surfaces. Let it soak for a while and hose her down, put a bag over the distributor and carb. If there's not enough slack on the heater hoses to clear the cover, remove it from the manifold, after draining coolant, or just get messy with it, your choice. After you get it up off the head, vacuum out all the crap that may still fall into the head. For gasket removal, I use razors, brass and stainless wire brushes and rubbing alcohol. I takes patience and technique. Do not scratch and gouge either gasket mating surface, but get it all off. If it ain't metal color, it's not clean. The alcohol is only to de-grease when you have all the surfaces clean. Do it right, or do it again.