alloy or steel spindle

[Avery08]

I'm working on an awd project.For various reasons I'd like to machine a new set of spindles to use corvette axle hubs.I don't plan to design a new spindle but to duplicate a mustang II spindle with extra area to locate the axle hub.A friend has owned and operated his own machine shop for almost 4 decades.He will be the one machining the new spindles.The mustang II spindle is a bolt on for my application and a popular design widely used,as we all know.Should we use 6061,7075 or steel to machine them from?