Valves were adj @ 29k and motor now has over 40k,HMMMMM?

You saying noise is high up in jug meaning high up in the cyl ,could be in head you you dont realize it.

Andas far as lifters go,they dont have to make noise dow low where they are housed,the noise can come from up top where most of clearance could be.

Have you taken a comp test or leak down test to verify if maybe piston skirt or rings are broken causing knock or piston is damaged in some way?

Did motor all the sudden start to use oil or show sign of using oil thru ex after this noise started?

Because if compression is good,no oil use etc it could be a busted valve spring that will not sho up on static comp test becasue motor not spinning fats enough to strees the spirng but with motor running it will make nose.i have sen that before too but not in a R*.

Maybe a rocker arm i worn out or broken.

Just trying to ensure you exhaust all other less evasive/less expensive possibilites before you take the plunge to tear it down without checking rockers,comp test,etc.

Good luck.

Scott