Hydraulic bellhousings (at least for our trucks) are all aluminum.
Used on everything from 6 cylinders to 454's, short of the problems one or two people have expressed on here, the aluminum ones don't seem to be inherently weak.
I believe Novak or advanced adapters sells an adapter bracket, if you were set on cast iron bellhousing (that's the other stock material AFAIK) adapter is your only bet I imagine.