Indy aluminum blocks are "cast aluminum, they are not made from a forged aluminum square block like most of the newer race blocks are that are called "billet aluminum"
If you think about all man made metals they all come from a big molten pot of that material that is poured into molds and then either stamped "AKA Forged" into molds that are the shape of the part the makers wants to finish into a part or the molten medal is poured into a mold and removed after it cools with no stamping of the parts, hence those parts are call "cast"