Duplicolor "Steel Wheels" was a dead-nuts match for original, unfortunately, the @$$*&#!$ discontinued it last year. If you can find a reproduction of Argent silver (commonly used on vintage musclecar wheels), it at least has a finer metalflake than most of what's being sold at present. All of the "aluminum" finishes I've seen are a bit too blingy compared to original. It's not a bad look, but the coarse metallic really stands out if you're trying to duplicate "cloud silver". You can always take an original item to a paint supply and use it to find a match.
Urethane wheel paints are thin and intended for DTM (direct-to-metal) application. They also resist gasoline. You don't really want to use primer on engine covers. It increases the tendency of the paint to chip and makes the chips more noticeable. Going the DTM route, your metal prep has to be perfect, media blasting and chemical cleaning are best.