Strange cast iron with the 3 1/2 " housing bore is what I have used for a good while.
35 spline requires it.
I haven't gone for the pro gear set up yet , but aluminum Daytona style pinion support , billet yoke and good gears ( I like U.S. gear ) and quality bearings ........... they are pretty hard to hurt.
I have a factory N case in the street car , but for racing or higher horse deals , aftermarket case is the way to go.
I have been intrigued by the aluminum case , but haven't done one for myself yet.
Never had a car or deal where it would have made the difference.