70 is good using a differential pressure guage. 80 psi is about the max that a person can keep the crank from turning. so holding 70/80 is pretty good. It's a leakdown test, you can listen where the air is escaping, and determine what's wrong.
In this particular case it's a 360 cubic inch aircraft engine. Has 550 hours since rebuild. (should have gone over 2000 hours)
Found the trouble to have been caused by a combo of two things. #1 leaded fuel, and #2 valve guides on the tight side, but still within allowance.
Lead buildup on the valve stem, caused stickin' valve, thus causing burned valve. (note the discolored stuff on the intake valve That's lead)
That's ok because he can get a complete cylinder assembly New from the engine manufacturer, including new piston, and rings, for about $1100 +/- a few bucks.
Now just exactly how izzit that lead is supposed to prevent valve troubles?