The new aluminum heads will flow more air
Since no specific head was specified you can't say this.
Plenty of aluminum heads out there that are crap and need rework out of the box, I suggest you google speedmaster heads. So when some say " the cost pf rebuilding an iron head" as an excuse tend to not add the cost of making sure you aftermarket aluminum head is ready to run.
Nor is there any actually data supporting the aluminum allows higher compression claims. Combustion chamber design is the major factor in allowing higher compression, iron hemi heads can run just as high a compression as aluminum ones. Assuming your new heads have efficient combustion chambers you can consider increasing your compression ratio.