I will give Marty a call tommorow" he is well known for his work being very good" 300 drag should be fine running this" as the guy I bought it from dragged raced a stv" but I will call him tommorow and ask about your question, sorry for the late reply
Talked with Marty Today, It is not hardened' Marty has done hundreds of these drive shafts, has a very good reputation, he said anyone can give him a call he will explain his process (727) 742 1235