Molecule for molecule, atom for atom, Iron heads are far more rigid than aluminium ones so are less prone to warpage.
Having said that I confirm Fido's comment.
A 7 & A 10 do not have inherit problems with their head gaskets till you start putting in really big pistons.
The only thing to watch is that you put some thick washers under the heads of the nuts on alloy .
Because the aluminium is less rigid than iron the bolt hole can collapse onto the stud which makes it very hard to remove the head & can lead to inconsistant clamping pressure between the head fasteners which will cause leaks.
