As far as tightening up the lash and knowing when to stop is try .002 to .004 tighter and look at the time slips. If the motor likes the tighter lash try some more, a little at a time until it stops gaining HP and MPH . If it goes from .026 hot to .016 hot and is still going faster I would probally stop thier and think about buying a bigger cam with better lobes. If it goes slower with tighter lash try loosening it up a little and see what that does
Good luck.