The "squish the lifter" advice will work, but not the way it's been described. Find a valve that's closed, not open, and put a hard push on the rocker arm with a pry bar, trying to move the pushrod back toward the lifter. After a minute or two of constant pressure, a gap will develop between the tip of the rocker arm and the valve stem, sometimes as much as 1/4". The oil trapped in the lifter body squeezes out slowly, allowing the rocker to back away from the valve stem. As soon as the engine starts, the oil pressure will cause the lifter to refill. The compressed lifter will clatter for a couple of minutes, then finally it will refill itself and the noise will go away.
A solid lifter will not allow a gap to develop, no matter how long the pressure is held on the rocker arm.
Jerry
