Help with Valvesprings and valve float. Noob

And yet, even when you adjust the “hi rpm” lifters to .002-.004 lash(so they can’t “pump up” and hang the valves open)...... they still exhibit the exact same problem.....and that problem disappears when the lifters are swapped for solids.
(Just like they discovered in that article).
I have done this on the dyno numerous times........ on several
different engine platforms.
Hyd flat and hyd rollers.

There’s a reason things like limited travel and Shubek style lifters exist........ and it’s because normal hyd lifters don’t cope very well with fast rate lobes, high rocker ratios, and the associated spring loads required to allow for high rpm use.

Sell him a correction kit........ see if it cures his problem.
If it does...... it’ll be his cheapest way out.