Swapping from iron to aluminum heads

They don't want more compression, they don't change compression all else being equal. You can get by with more compression, is the best way to put it. Don't worry about the compression. Worry about flow. It's the flow of the better ports that adds the power. Lastly, if I had the money to buy aluminum heads, I would also make SURE I had the money to have them professionally ported to take FULL advantage of them. Otherwise, you're spending all that money for less than 100 HP and that's kinda stupid, IMO.