Just remember to remove the tape and paper promptly after cleaning. There always seems to be some leakage past the tape so getting any soggy towel out is a good idea. Tape left too long leaves residue of it's own that can be hard to clean.
I've used oven cleaner on a lot of aluminum heads in the past with care it will brighten and etch a lot of oxidation off. You can't leave it on long and do so in a ventilated area. Also aluminum brightener from Napa or any parts store will do the same thing.
I don't use simple green for anything around a running machine anymore. Stuff stops working after you wash an engine bay with that stuff. Fine for bare metal parts. That stuff is nasty. I have some hippie friends that use it because they think it is environmentally friendly. It was named way before people called stuff green for that reason. Oven cleaner is a base, not an acid. I have a friend that has a caustic tank, heated for cleaning SBC blocks. It will disolve an aluminum engine block in short order.
The two things I have had luck with are distilled white vinegar 10% if you can get it and be careful. Aluminum wheel cleaner can work as well. And good old elbow grease always works. Wire brushes, scotch brite pads in a small angle grinder, dremel, etc...