4140HT would be an excellent material to use for this application but I am uncertain of the exact procedure for oil quenching. I don't think the propane is going to get you enough heat unless you introduce some oxygen - like in a kiln arrangement. Is that what you are proposing?
Most of my experience with heat treating this material is carbon Nitriding and that was left up to the heat treating department. I am positive Google would yield substantial results on methods and specifics.