Thanks Tom.
Would revving the engine like this have done any damage?

It is never good to rev up a motor beyond the red line. The danger is that the valves will go beyond the limit of control by the springs and "float" away from the cam shaft. When that happens the valve can impact the piston when it comes to the top of its travel, bending or breaking the valve. If the valve gets bent it will not seal correctly (or worse). improper sealing will lead to a burnt valve eventually. If the bend is severe you will have a heavy miss right away. If it happens to be slight you might not have much of a miss at first but soon it would get worse.

Is the car missing at all? If the idle is completely smooth you may have gotten away with a foolish act by your friend.

If the valve had broken there would be piston damage too. A bent valve could also cause piston damage as well.

If the car develops a miss in the next month or so you will have to do more investigation.

Good luck.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Would damage occur even if it was in the red line for less than a second?
Its not missing or anything.
The idle is smooth.