I've never seen that happen on that motor. Maybe if something happened to the cam or crank timing gears throwing it out of time causing the pistons to hit the valves and that caused the push rods to bend. I don't think the oil pump, bad pushrods, or ether caused that. You could try removing all the push rods so the valves stay closed and apply compressed air to the spark plug holes, then listen for any major air leaks coming through the intake manifold. If so, then it has a bent valve and the head has to come off. If that's the case then the timing gears need to be checked also.