You guys have to read the books, I have been thumbing through Donohue's book and it is full of great stories.
Here is a quote, not about the 917, but about the decision Penske made on which cars to run in the first IROC racing series. Fords, Mustangs, Camaros, Porsches and Javelins had been considered.
Finally the 911 3.0 Carrera RS (a car we never got in the USA) was chosen, modified with a racing rather than the street engine.
They were chosen because Penske wouldn't have to build them, they were relatively cheap, they would be truly identical, and most important dead reliable.
Here is Marc on the reliability:
"Dr. Fuhrman had told me once that the car couldn't be broken-as long as it wasn't over-revved and as long as it was shifted correctly. And that was really quite true. They come with Cam-Am brakes, dry-sump lubrication, fuel injection, good ignition, oil coolers, stainless-steel exhaust pipes and a not of nice things that only racing people can appreciate. "
I like that quote.
Building cars racers appreciate is what made the brand!!
As you probably know, Dr. Fuhrman was CEO of Porsche at the time and also was the designer of Porsches first true racing engine the 4-cam Type 547 used in the 550 Spyders to the 904. The last of the track-racing CEO's.