Hi, Chris.
I'm not aware of any information that could confirm this. In fact, I'm not aware that the 70 had a failure of the crownsheet.
Ken Martin has convinced me that 70's conversion to oil was an experiment to study fuel efficiency.
While this could have been done on any of the engines, there might have been a reason to select the 70 and that may have been it. I'm sure they wanted one of the B-4-D class engines for the study.
Good question, Chris. How do you know of the crownsheet problem?
Mike