Removing the side cover isn't necessary. If you get a valve fully closed with the engine stopped and put a constant steady pressure against the pushrod side of the rocker arm with a pry bar or a long screwdriver for a couple of minutes, a hydraulic lifter will collapse and the gap at the valve stem will increase- - - -up to maybe 1/8" or a bit less. It doesn't require much force, just a moderate amount of tension for a while. A solid lifter will not collapse, no matter how long the tension is applied. Once the engine is started, a collapsed hydraulic lifter will rattle for a few minutes while it pumps up again.
Setting ignition timing with a vacuum gauge is an utter waste of time and effort. It's sort of a "measure it with a micrometer- - - -mark it with chalk- - - -cut it with an ax" procedure.
Jerry
