RAMM already posted about using a hydraulic roller. I wouldn’t do it either. I hear about guys turning those junk lifters 7500 plus but I’ve never seen it done, or done it myself. If you use the thickest, most gooey oil you can find, get around 180 on the seat and 500ish (or more if you can) over the nose you might get it to 7000 before you start seeing issues with valve control. Maybe. And that was using some lightweight, hollow stem custom built 5/16 stem valves.
By the time you do all that, and open up the bearing clearances for that thick oil you could just use solid rollers on a hydraulic lobe and be far better off.
