Same block same cam same lifters- safe to reuse? Setting preload?

It'll take about 1000 psi for a lifter to pump itself off a valve seat. The only time a lifter can take in oil is when the check ball is open and that is when there is no load on the 'flat' lifter, ie on any of the other 3 cycles of the cylinder during start up. Once its 'pumped' to zero lash the check ball closes and no amount of pressure will allow any more oil in, the lifter is hydro locked and acts like a solid lifter. No noise, perfect. The only time your going go get a lifter to accept any more oil is if you start flexing pushrods or start floating valves, allowing the lifter plunger to extend past the point of the valvetrains zero lash as there is no valve spring tension on plunger to keep the check ball closed.