Beautiful example of Duke's first needle bearing Combat Special. That engine also introduced the square intake that Duke stayed with for the duration of his combat engine involvement. "Front loader" was my nickname for these when they would come in for repair back when I was at Fox. We didn't have any more .35 cranks to repair with (if crash damaged/etc), so I would fit them with a 36X crank and the result was a "stroker" engine.
As for breaking the crank: Not a problem if you don't go crazy with the nitro. The engine SHOULD outlast you.
For sport flying and the general health and longevity of it, I would suggest 10% nitro and only castor oil.
Attached is an engine review by Peter Chinn from back in the day.
Enjoy!