I don't think you can measure how much a pushrod bends in an engine since there is a lot of stuff in the way plus the pushrod moves around as the rocker arm moves.

You can set up a test rig with a hyd cylinder pushing on a pushrod. Put about 1000 lbs of load on the pushrod and use a dial indicator at the center to see how much the pushrod bends. They aren't going to bend a bunch, maybe a few thousands or so.