Stock Hydraulic Lifter Preload Spec?

Actually the biggest downside of running only .020 preload, on non-adjustable arms, would be what to do as the preload relaxes to zero, over the course of time.Sooner or later they will start to clatter, then it will be time for new pushrods again.
The upside of running .020 is the engine will rev till the oiling system fails, and then you have to put in new parts again.
And if the lifters do pump up no damage can be done. It just won't idle for a minute,lol
So, if you can't afford adjustable arms, and you're oiling system is stock, then Judging by how mine are holding their setting, I suspect .050 is lifetime plenty.That's an educated guess, no more than opinion.