The original was Tuftrided...and yes, it is a nitride surface hardening. I have not found any modern source for tuftriding. I think the chemicals used were banned. The closest hardening you can get would be ion-nitriding, available in any large city which supports an aviation industry.
If I were building a race motor with a very high-dollar crank I would ion-nitride it. In the TR, a good used crank is only $200 to $400. I wouldn’t spend the time or money nitriding a low dollar street crank.