Painting cast aluminium engine

I would definately say to not rule out powdercoat paint. If you have it available, it is very easy to do. When I do things here, I use a heat gun to heat up my metal, then dip or pour the powder on your piece. Or you could Google a 'homemade powdercoat fluid bed' which are quick, easy, and cheap to make. From there, you can use the heat gun again, or put in either an over or toaster oven to cure and harden. But, the heat gun is the quickest. Just be sure to tape off any openings you do not want painted, then remove the tape either before curing, or immediately after (only if using heat gun). I use this process on my fishing equipment with great success.