Why does it matter top or bottom the rockers are off and there is no f!@#ing around just hook up the air, the piston will go down and there will be the same air pressure.
SO he won't have to pull the head off to get a valve out that's dropped all the way down in the cylinder. If he turns each piston up to TDC as he's working on them, he needs no rope and really no air. BUt since he HAS the air, he may as well use it.