We use orange cleaner on our engines. We spray them down good before we wash. A few times a year we hit them with S-100 to keep the black looking good.
I bought some aluminum wheel cleaner at Auto Zone the other day to clean the wheels of my car........man it cleaned every bit of brake dust/grim, road grim and salt spray. Might try getting some of that and shooting it in a test area.
HD sells their brand of engine cleaner in a spray can. I got a free sample can but have not had a chance to use it so can't speak to how well it works, but it might be worth a try. My experience with their cleaning products has been pretty good for the most part.
I use bleach white for stubborn spots. Put it on a rag, do not spray it on. Wipe it good with a soft cloth. Clean with a wet cloth. If it does not come off then I doubt if you will get it off.