The instructions that came with the cam (Lunati) say this for adjustable rocker arms (no specific number mentioned):

On engines with shaft-mounted adjustable rocker arms, we recommend fully backing off all adjusters prior to
installing the rocker shaft assembly. Be sure the pushrods are properly “seated” in the lifters and rocker arms before starting
your adjustment procedure. NOTE: Improper adjustment of the rocker arms can cause the valve to hit the piston upon engine
rotation!

On hydraulic lifter cams, rotate the engine in the normal direction of rotation until the exhaust valve begins to open. At this point,
adjust the intake valve to ZERO LASH with no pre-load at the lifter, then tighten 1/2 more turn. Rotate the engine again until
the intake valve has fully opened. Now you can adjust the exhaust valve to ZERO LASH, then 1/2 more turn. Repeat this
procedure until each cylinder is completed.

But they do specify an actual amount of preload for non-adjustable rocker arms:

On engines with non-adjustable rocker arms, you must have a lifter pre-load of .020” to .060”.