Superbird would be cast iron with "maybe" a few exceptions but I have never seen an aluminum on a bird that was actually documented.
I'm not a wing car guy, but I heard GG say at a Mopar show there are few SBird's documented. To avoid me passing on incorrect info, I'm just repeating what I heard GG say about 20 years ago, I have no proof it's true.
I have a '70 Cuda, first rode in it in '75, bought in '89, SPD first week Oct, Edelbrock intake. I asked the original owner about it, he said yes it's a cast iron intake by Edelbrock. He knew the '70 440-6 came with cast and just assumed it was made by Edelbrock. Appears to have never been off the car.
There's a '70 RR 440-6 near me, SPD second week Oct, Edelbrock intake.
Just like the statement GG made about SBird's having Edelbrocks, I can't see how any 440-6 can be documented coming thru with an Edelbrock intake.