I look at e bay all the time in order to see what is for sale. There have been a lot of R5/P7 and now R6/P8 engines listed. I've noticed that many of the R5/P7's are for sale between $6,000 to $11,000.

The dynamometer sheets indicate maximum power at 9400 RPM with a flat tappet camshaft. The things evidently make 860 horsepower there as well.

How do they do that and keep the motor alive for 500 miles?

I've heard they run ceramic type lifters so they can use more spring? I would think they run a very high rocker ratio also to get the least resistance to cam opening. Ti valves, retainers, just guessing here though.

there is a surface prep used also- nitriding? crs. you can order this treatment from comp, irc (crs, remember?).

They imbed the valve train with 100 dollar bills.

Comp Cams Plasma Nitride coating.
Here is a picture, of a cam I had done.

Bullet Racing can do it also

i would say after 500 miles they put a new cam,and springs in it...not sure

After 500 miles , most of it winds up on ebay.
The parts are better now, than when I had " inside " info on the sport.
But back in the early 80's , after a 500 miler , most of it went in the scrap bin.
Back then , I was pondering what they did with all their old parts..........thinking there might be a home for them in a less demanding environment.
And today , they devote a lot more resources to R&D , so there are a lot of parts that have never run a lap getting sold.

20 years ago, I knew an metallugist that did damage analysis for Hendrick. When he told me the spring pressures they ran, I asked how the cam and lifters survived. He said the cam cores were made of cast iron and were intended to be sacrafical. Since the lobe has more surface area than the lifter, it took longer to wear the lobe than the small contact patch the lifter has. The cams did have problems with pin holes in the core casting and the had a lack of tortional strength. He showed me cam that came out of the #3 (not a Hendrick car ) that broke between the 6th and 7th lobe set from a pin hole and tortional twisting due to the lifter loads from the high spring pressures.
This was years before ceramic lifters came about and the 9400 RPMs they turn now.

They use powdered metal cam cores with DLC coated lifters nowadays. I think before that they were billet steels cores with the same lifter. Some of the Super Stock classes here is Australia mandate the use of flat tappet lifters. Those racers kill a set of springs a meeting and running through the traps anywhere between 9-10K.