were you talking to rulebreaker about this??? My wife has been machinning for 15 years and she can quote you a turned up version for you, if you supply her with all dimensions.
Then you can send out to spline and heat treat.
She can use both pieces and press them together and weld them, but, this weld area makes for a very possible break area. The shaft can be bored out, but, because this shaft had already been hardened, cutting a key in it is just about impossible- the hardness makes it very difficult on the cutter and the machinist must take several small cuts at a time to achieve this-thus this is a very costly way to go. U may call her @ 231-775-2370 her name is Julie