Back to the rattling from the engine

[geeaj]

If it isn't rattling at startup or during part or WOT throttle, then its not likely your oil pump. During both scenarios, alot of demand is placed on the pump to "push" the fluid.

I would suspect a cracked or scoured bearing as far as the bottom end. Also, have you checked your timing? Stretched timing chain can throw off your timing and cause lots of performance loss. When you took off the valve cover, how did the chain look?