I use the crock pot method. Works great. On really really bad gunk, you might have to use a tooth brush or a scribe to pick if off. The engine will look like new. If there is a carbon on the valves and cylinder head, I'll use a wire wheel or wire crown brush to clean it off. You just have to be real careful with the valve stem keepers. They'll spring clear across the room and be lost for eternity. Some guys do that job in a plastic back to keep from losing them.
Edwin