My old 5l in the Ltd is starting to get a bit noisy up top. She has done 420k, but no bottom end noise and no smoke! Wanted to know if there is an easy fix to quietening down the rockers/tappets or lifters. Never worked on a V8 before, and dont want to mess things up! Are the valve clearances adjustable on this model? Apart from this the engine is great, and the car handles like new. Great car! Thanks for any advice in advance!

Sorry, there's not really an easy fix and the valve clearances are not adjustable.
How often is the oil changed and what oil do you use?
How's the oil pressure?

Oil has not been changed in a while, but it is still looking ok, not black. What oil would you recommend? As far as I know the oil pressure is ok, the dash doesnt have a meter so dont know for sure. When it is first started there are no rattles, but as it warms it is more pronounced. Its not really bad, but just wanted to try and catch it before it gets any worse. Was thinking about an engine flush and changing the oil and filter to see how I go. If that doesnt work, what would be my next option? Thanks