Have a look at this:
http://www.sohc4.us/forums/index.php?topic=11044.0You better think twice before painting the engine. I did some test with CRC Alu Zinc -available in Spain- and it looks superb, but a couple of minutes in contact with gas -even when it had dried for more than a week- and the paint peeled off. General consensus is that paint from a rattle can has dissolvents to let it last long, and therefore it doesn't hold up well. The same goes with painting a gas tank; it's not the same to paint with a rattle can as a professional job with paint, hardener etc.
I bought a spanish made Sanglas bike a year ago. Parts are in the painter right now, but there was something I didn't like: one of the previous owner decided that the dirty, sandcast look -seriously, engine parts are sand cast- didn't look well so he sprayed the whole engine with zinc. The carburettor doesn't have choke but depressor, so every single gas spill left stains in the covers. As I had the engine dismantled, I got myself a big rubber basin, put the engine inside, spray with gasket remover -much stronger than paint stripper-, and let the paint bubble. But scrubbing with a brush won't help, it would just change the paint from one place to another. I had to use gasoline to clean the softened paint, change the gasoline, and do the same two or three times. I don't have to tell you how hard is to remove the paint from between the fins.
Seriously, if you are not 100% sure of the outcome, don't paint your engine. You have plenty of time to paint it, but once done, it's not that easy to revert the situation.
Raúl