Hi volume oil pump vs standard volume pump

The lifters were new but I had them for years already. They came in a blank box however so no telling what brand they are.
It's no problem to run solids on a hydraulic cam, but you need to run a very tight lash of around 0.006" and pay attention of hot and cold settings (cast-iron heads & engine).
I've contacted CompCams about this too years ago when they told me to keep the lash tight and make sure the lash is taken up before the actual ramp starts on the lobe. Otherwise you will be hammering the valves and shorten valvetrain-life.

I hope the solid bodied mechanical lifters will take care of the low (warm) oilpressure in my engine.