I just did this today, used some APC at 1:4 a light spritz in a few spots and agitated with a 1" boars hair brush. I did not do every single spot, just the ones I could safely reach, knowing that I could reach with a towel to wipe off. For wipe off I sprayed some ONR at QD ratio as APC does foam and cleaned up as much as I could. In hindsight, if APC did not foam it would have been easier, not that this was difficult in any way.
I then used Wolfgang exterior trim sealant on the entire engine bay where I could reach safely and WOW is all I can say. This was the first time I have ever done anything in an engine bay. Been way to paranoid till now.
It's pretty much my adaptation of the "how to cosmetic engine detailing" linked above by LED detailing.