Non caustic oven cleaner and a paint brush to break it all up - worse case scenario use an old tooth brush to get into the tough stuff. Strip the head first and make sure you separate and ID valves and springs so they go back where they came from. This will also help if you run into a problem and something is showing unusual wear (valve stem, seat etc). A pressure clean afterwards and it should be squeaky clean. Do the rocker cover and intake manifold as well. There is an oil gallery that is plugged up next to #4 exhaust port. Take the bolt out and flush it with brake/carby cleaner and then force compressed air through it so there isn't any gunk waiting to ambush you when you put it back together.

*yeah don't use acid based alu cleaner/wheel cleaner - it will stain the metal badly. And definitely DON'T use anything caustic or you won't have a head to bolt onto your engine