Royale RP21 Rear Outer Stub Axle

I've been working on learning a CAD system called OnShape. It was recommended by a teacher from the local community college.
Needless to say, it's taken this paper-and-pencil draftsman a lot of hours to figure out how to do solid modelling.

One of the features I like about the way Royale designed this part is the way the British square machine splines washout, almost like spokes. Running a radius gauge on them, it appears the cutter was a 2 1/2 diameter profile cutter.

I have no idea what alloy this is made from.

From the car designers: I assume 4340 steel would be at least as good as original?

CNC guys: I've seen where CNC turning centers can broach keyways. Could they do the splines with the washout feature?