The motor compartment is Galvanized steel. With a color change and wanting a long lasting paint job...I suggest stripping all the way to metal. When I did my sons I used a epoxy primer over clean metal. ( that is what will be used on top of aluminum as well )...then high build ( 2K ) primer over that. ( that's what I did and it worked well for me ) I shot 2 coats of high build...then sand and sand and sand and sand and....sand some more....more primer if needed to get it all dead flat. Did I say sand?
Shooting color and clear are the 2 easiest parts of the job. 2 coats color...2 coats clear...I used more clear as I wanted to have lots of clear to sand smooth. Flash times ( time needed between coats ) are very important.
There are tons of help on the net.
Paint Your Own Car Spray Guns Automotive Auto Body Forum was helpful and here as well. I also bought a book on painting cars.
Not sure about spray cans...I am sure they are available but I am not sure its as good a paint as it could be.