I don't agree. Even on a stock engine, the difference between correct cam timing and cam timing that's a little off, more or less sort of in the ballpark, I donno, whatever can be felt in just about every aspect of driveability and performance, and seen every time you calculate your gas mileage.
I tend to agree. While we all know the slant 6 is a great engine, they need "all the little parts" to the puzzle to run really strong. Every little detail helps.