If your in the sticks, so to speak, I can't see nitriding and having a factory oe turned is cost effective. You will still not have the rolled fillets (the radius on the journals). Turnign the journals down is one thing, but for a quench build engine, you should have it indexed and stroke corrected, because a varience on either of those of .005-.010 can create problems and wont be found until the assembly phase. Nitriding gives some strength but is primarily a surface treatment. Done properly it can go deep enough to not worry about it if you are turning the journals down .010. If you are truly looking to make a factory crank better, I would first cryogenically treat it, then machine it, then nitride it. Cryo goes completely thru the material, and changes it's structure, making it much stonger. However like heat treating, it will change shape, so you have to do it prior to machining. (and yes, machining it gets much harder...lol)
