Shooting clear on aluninum
I used the clear coat (forgot the marketing name) from POR15 on my HD Sportster's aluminum heads after I polished them up.
After the clear coat, they looked slightly duller than the polished aluminum, but have pretty much stayed the same form 10 years. (unlike the weathered look before I polished them)
http://s957.photobucket.com/user/emsvitil/library/M19 Sportster Rocker Box?sort=4&page=1
The POR15 clearcoat I used was the 2 part stuff, I think they have a 1 part.....
I used a hobby sprayer from Harbor Freight so if I ruined it (i.e. clogged it up) it wouldn't matter as I got it for $5 or so.
Make sure you clean out the sprayer before the clear coat sets.