It was noted by the OP that the oil was black within the 40 miles put on the vehicle. Nothing says burnt oil than to tight of tolerances. The intermediate bushing might not have been seated completely,wear is shown in the picture . Might be some of the brass, probably wouldn't turn the oil black. I would look at the bearings. Good luck with the engine builder. The building of a engine , any engine requires knowledge of tolerances, and proper assembly, it doesn't matter if it is a Chevy, Ford, Mopar or Briggs&Stratton . There's know excuse nowadays with the internet, you can look up anything you need to know, even proper rocker arm assembly. So with that being said, if you did all the right things upon startup and the engine still took a $hit be prepared . Write down everything you found wrong right off and made the engine builder aware of. What you did to correct the problems. Did you follow correct priming and break in procedures. Who told you what to do and how to do it.