Like Ed, I adjust the valves while engine is running and at Normal Operating Temperature. I have bent feeler gauges and I constantly slide the the oil lubricated feeler gauge around (while making slight valve adjustments) until I feel a slight drag.
I use a 3/8” ratchet with extension, universal joint and socket. The universal joint helps absorb some of the rocking motion, as I’m not that good of a dancer.
Switching topics slightly:
A while back I hauled a couple loads of gravel with my truck in AR (trailer and gravel weight of 8K-8.5K pounds). Then drove my truck (pulling my camper back to KS) after another warrior weekend in AR, and I noticed a faint slapping noise while pulling the truck into the garage.
The noise reminded of a loose cam chain I found on a motorcycle I was riding in college, which I was able to remedy after making adjustments to the cam chain tensioner.
Back to my truck, I’ve never heard that slapping noise again. It was really hot that day and I was towing my 4K pound camper in the KS winds. I completed another full tuneup and I didn’t find anything out of tolerance.
I often wonder if that noise was my cam chain, as I only have one gear on the cam and when I put all new gaskets on my engine (except head gaskets) about ten years ago, I noticed the cam chain had plenty of slack, but it was in tolerance. I thought about replacing the chain at the time, but had read that a new chain/gear set also has lots of slack.
I later learned that there is a double cam chain/gear set available for our engines, which I plan to incorporate one of these days.
Good luck on your continued noise research. Hopefully, it’s not anything of concern. In the meantime, great opportunity to learn a lot about these unique engines.