Oil Pump shaft broke

FWIW........I am using a hardened drive with my Melling 72HV in a mild build 340 on the advice from an engine builder I know. Having said that, for ***** and giggles, I took an OEM drive and mounted it in a vise, and used a pipe wrench to twist it to the point of failure. And, I've got to say, it took a LOT of force to break it. I find it hard to believe that it would take that much force to turn a 72HV.