Reading up on the milli volt method in the archives and applying it may give you some indication of what may be going on. Before going that way I would make sure there is a clear line on the return fitting on the injection pump and look for any amount of air being processed with the fuel. No fuel flow would indicate the supplied fuel pressure is too low to open the return relief valve. I take it your motor mounts are in reasoable condition as well.

On the 616 engines to me it is important to have 15-19 pounds fuel pressure present in the base of the injection pump. . May be worth checking this after you get the idle smoothed out.

As for the dynamic running effect of the differance in low piston speed compression readings you are seeing. I have never totally made my mind up when the compression numbers are in the area you have. Certainly I would not suspect there is enough varience to give extreme shaking at idle. Simular to a cylinder missing. Or anywhere even remotely close to that..

Your quantitive element spraying test is okay but will not address the sequental timing of the injection pump elements. The milli volt method done properly is a better general test to determine what may be going on in my opinion.It will indicate where the problem or problems are..

Closing off the return line is another quick test to see if there is any differance in the idle. No change at all might indicate fuel pressure is really low. Much smoother idle would indicate the pressure in the base of the injection pump should be checked. This is redundant to some extent since all 616 engines should have this checked in my opinion.

The milli volt methods use was designed to reduce guessing what is wrong and buying parts on speculation. It takes a little effort to use it properly but it will not mislead if done properly. .You could do a cylinder drop test but it is not sensitive enough to give any real indication in your situation I suspect. That test is where you loosen one injector at a time looking for an abnormal drop compared to the other cylinders..

Much of the above is based on us not being working mechanics. We have to substitute effort for experience.