I think much of the break-in period is for the drivetrain and not the engine.
Certainly, with roller cam engines there is essentially no cam break-in. The rings seat quickly (that is the main thing that needs to 'wear-in' to fit).
The other purpose of break-in is to give the owner a change to HEAR and FEEL problems before damage is done.
If something wasn't properly tightened at the factory, comes loose, was damaged during the build, etc.. That 500 miles is so you feel the wheel get loose before it falls off and have a chance to stop the car (since you're not driving over 55, right?). At 160, it's just going to come off and you're just going to die
Or, if you have a rocker problem that barely becomes noticable at 3000 rpm.. Good thing you took the time to notice it before blasting to 6000, eh?
Drive it like a race car - maintain it like a race car. I won't go that fast in a car until I've checked the torque on all of the critical fasteners. It doesn't matter whether I built the suspension or GM built the suspension. After 500 miles, checking the torque and marking the fasteners with a paint marker is a good idea.
With all of the sensations of a new car, it can take a while before you notice very subtle problems (especially if they are slowly emerging).
I think letting the syncros and differential break-in is also a good idea..
If the vehicle's exhaust is loud, it's just that much more difficult to detect problems before they become serious. It's like detonation in a race car - it can be impossible to hear until it is too late.
When I break in a new race engine, I give it 30 minutes in the driveway to look for leaks and listen (but the exhaust is really loud). And since I am the warranty, you can bet I watch it like a hawk. Then I go flog it and constantly check and listen for problems. There's a lot of anxiety until you give it some quality time at 7000... And then you just don't worry about it.
So I agree.. The engine can take high rpms soon after delivery assuming there are no defects. But taking it easy isn't a bad idea..