What I did was to leave the engine right where it was, remove the water pump and then pour CLR in there until it was within 1/4" or so of the pump opening. Then I straightened out a coat hanger and bent about a 1 inch L at the end. Then I let the CLR sit there overnight, drained it, neutralized it with soda, repeated and this time I scratched around at the #6 cylinder as best as I could with my coat hanger. Eventually it drained okay through the petcock at the rear of the engine. I left it at that. You can buy vinegar up to 45% strength (which A---you must use in a garage with the door open only and maybe put a fan in there too and B---you don't want to leave in the block for more than about 15 minutes because it is very nasty stuff. Soda will neutralize what you drain off also. Or you could go water greasewood bushes with it. I haven't found anything that damages those. Good luck!
