In the Citation we have taken an engine in the 2,000 mile range. The only reason that engine came out at that time was because the crappy surface at Sebring tore up 4th gear. That was a zero mile engine straight out of a bike, no prep work or blueprinting or massaging.
What kind of oil temps and pressures were you getting? I think these engines will go thousands of miles between rebuilds as long as people keep the oil temps down and the oil pressure up.
Also, restricting the motors in the future may turn out to be a good idea. Brandon and Niki are already near the pointy end of the Atlantic grid and these cars are going to get a lot faster.
The CRB has always maintained that they can add restrictors any time they want to. If they decide to go down that path, I really hope that they appoint George Dean the benevolent dictator of FB and pay him to determine our restrictor sizes. I trust him.