I don't think there is an industry specification that defines a manufacturing access relief for broaching or plunge EDM..
You can look at industry standard broaching tools to estimate clearance. Ultimately, each sourced manufacturer is going to different capabilities - a design for manufacturing review will get you the advice you need for the clearance details.
That plan will drive the costs up - design for an adequate FOS if you have the material. Don't over tolerance..As the shaft is critical structurally I need to be able to design the relief accurately for use in FEA software.