Re: Break in question
I've had my fair share of experience with engine builds. The thing that really makes the difference is cylinder loading and heat cycles. I would call it "spirited" acceleration. Not necessarily WOT romps on the stupid pedal. Doing so increases cylinder pressure pushing against the rings and valve seats. That goes for any engine, any material block or heads.
The gear faces are a different story. Gears can take several hundred miles to go through the "work hardening" process. Essentially, forging the metal under heat and load to complete the finished faces of the gear. Too hot and the metal gets brittle and not hot enough can leave pitting.
Anyway, done geeking out but that is why I suspect drive train and not engine for the difference.