Lifters and Oiling

Would a weak oil pump cause the Cylinder #2 Exhaust lifter to clack? I ask because I recently collapsed that lifter due to overtightening.

I overtightened it because it would make a very audible clack, I would check the preload, and it would be low. So I'd tighten it a half turn, and so on, about three times. Finally, after running on it about 6 weeks (still clacking...) it completely collapsed.

When I add in the following facts:

- Engine is running about a needle-width-and-a-half hotter than normal,
- When starting, there is a delay in the oil pressure light turning off,
- The oil pressure light came on while going down a large hill the other day

I think I have a weak oil pump. Would that starve that lifter in particular? It's a corner lifter, so it would make sense that it's at an extreme in the oiling system.

If I replace the pump, should I get anything special? High volume? High pressure? The engine is a 340 that rarely sees anything above 3,500 RPM.

Would the weak oiling have damaged anything else too traumatically? On the extreme end, should I be considering camshaft replacement? I've put less than 2000 miles on it since the lifters were installed, and less than 1200 miles since I noticed anything funny.

To remove the oil pan and access the pump, does the engine have to be lifted off of the mounts to clear the windage tray? The vehicle is a '71 Plymouth Duster with the K-member from a '73.

Thank you!