The advantage of aluminum would be less weight, which for the street, you really dont need to car about much. The other is that you can run a little more compression without fear of detonation, but as you said, you dont know what you have now, so what's the sense? You really need to know what you have in there, compression wise, heads and what have been done to them, all the details. You cant possible start changing things around without knowing for sure what you have. You'll just spend the rest of forever changing out parts and wasting more money. When you buy a cam, they ask you what your c/r is....what do you tell them? You cant just buy any cam that sounds good. You have to match it up to your engine combo. Same goes for the rear end gears, carb, intake, everything. If you have no idea, how can you even start? Im not trying to be negative, but it sounds like you're just pulling straws, and lets see what happens. Your iron heads are fine for the street, and will let you run much more HP than you'll ever need on the street. Many race only cars are running iron heads. GM made some fine flowing heads, so in my opinion, that would be a huge waste of money. Cant you find out more info from the guy who built this engine? You really need to know what you have for c/r, pistons, rods, etc.