I'd suggest thinking about using a brushes rather than rattle cans. There's no overspray problem, paint coat thickness is better, rough casting of engine hides brush marks, and, you can do a little at a time. I would use rattle cans on the sheet metal parts (valve covers, oil pan, etc.). I've found the cheap foam brushes work great. That's what I used to paint my exhaust manifolds they look great. Just a thought.
