I wish I knew what it looked like, because it's been a long time since I have work on a chevy. See on the ford we have a arm that comes out from the pump and goes inside the engine to a little off set metal ring on the front of the cam. and that is what pumps it. I would say take the pump off and hold the rod, and have some one turn the engine over to see if the rod is moving. I don't know maybe that rod is a differant length
for this motor? Kurt