Since I'm assuming that you'll be racing with it, if for no other reason than weight savings, I'd say run aluminum. Also, as stated before, becuase of the thermo-dynamics of aluminum vs. iron, they disipate more heat and allow you to run higher compression ratios before detonation becomes a problem. They are obviously more expensive and there's a reason for that....

That being said, I'll be running cast irons on the flaming chicken because I personally couldn't justify spending that much extra money to get the aluminum Edelbrocks. However, if I find that the motor has detonation issues on premium pump gas....well, I'll have little choice but to make the switch.

Good luck,
Dutch