Try tapping firmly fore and aft on the shaft and weight. Keep the shaft wet with penetrating oil while you tap on it. You can hit pretty hard, but not like you are trying to drive the weight through the manifold. When the shaft moves a little, squirt more oil and tap in the other direction. Twisting the weight usually doesn't work until the whole thing begins moving. I haven't done the replacements you are thinking about, so no comment there.

Harvester