Get one of the cylinders on the compression stroke with both valves fully closed. (Pull a spark plug and tap the starter until you can feel a puff of compression with your thumb over the plug hole to find the compression stroke). With a long pry bar, push the rocker arm down against the pushrod and hold the pressure on for several minutes. If it's got hydraulic lifters, the clearance at the valve stem will slowly increase until it's 1/4" or more. As soon as the engine starts, the clearance will go away after the valve rattles for a few seconds while the lifter is refilling with oil. If the clearance doesn't change after some time with pressure applied to the pushrod, you've got solid lifters.
Jerry
