O/T What material would you use for new axle shafts?

[BRENT in 10-uh-C]

This is a little off-topic for a Model-A (-unless you want to consider the first-generation Model-As too ) but I am wanting some opinions from those who have some experience in machining some of these metals.

I have an upcoming project where I need to make a couple of new rear axles for a early brass-era automobile. I do have one to use as a sample so I am not starting totally from scratch however I am trying to determine whether I want to use 4140 or 4150, -or whether to use something like A6 or D6 to make these out of?

The hubs are not tapered but I will need to spline one end, machine a shoulder on the opposite end, a keyway for the hub, axle threads, and two bearing carrier surfaces, ...so there will be some machining involved. Whether to start with something I can anneal prior to the machine work, and then harden afterwards, or ???.

The other issue of uncertainty for me in this is it appears the sample I have is made from a mild steel based after drawing a file on it. Whether this one is an original axle from the factory, -or a 'blacksmith-built' one to replace a broken factory one at some point along the timeline I do not know. Since this is roughly a 20hp vehicle, maybe it does not need a tool steel strength axle but on the other hand, maybe they would have used something different had the metallurgy technology been better back then? Thoughts??