I have seen the bent pushrod thing in 235/261 engines before.One time it was a valve sticking in the guide that caused the pushrod to bend.Another time the failure appeared to caused by lack of oil to the head, the push rod was blue at the end.Check the ball on the end of the rocker adjustment screw.Does it look like a teat with a nipple or is it still round and smooth like a new one??Does the rocker tip that contacts the valve have a deep groove worn onto it? Unexplained bent pushrods usually go with the worn rocker arm parts.I think piston to valve interference on a stock engine is unlikely .As Jim says, they dont bend on their own.Your local machine shop will carry replacement rods or Patricks has nice tubular ones for the same money as stock forged ones.