You cannot expect an accurate measurement, unfortunately. You need to figure out "something" to do about the hydraulic lifter plunger. I believe the only real way to do that is going to be removing the intake, valley pan and flipping a lifter upside down. Otherwise, the lifter plunger will give you inaccurate measurements, since it will compress. Maybe @IQ52 Jim Laroy knows an easier way. I cannot think of one.....unless you can reach through the valve cover area in the head and do it.
