I put 20w50 in as standardIt would be mostly pointless....a new camshaft, new followers and new pushrods plus the top end gaskets are not overly expensive at the end of the day...but is about 2 days work
EDIT: Thicker oil as Henry suggests is just masking a problem...and at times, thicker oil has difficulty getting into the tappets in the first place, if they are a little gummed up!
Give us a clue what area are we talking about?I’ll give it a go, I may put some Wynn’s hydraulic valve lifter in it as well. If you see a Blue 2 door Range Rover in the lay-by give us a tow.