I've read threads on here about timing by the "drip method" and optimizing timing by reading the millivolts on the glow plugs, etc., but one thing I haven't seen is much on timing the IP with a meter.

As many already know (though some may not) there are two basic types of timing meters for a diesel - a "lumy" meter and a "pulse" meter. With no spark plugs there is no electrical "timing event" to trigger a regular inductive timing meter like ones used on gassers, so something else has to serve as the trigger.

With a luminescent (lumy) meter, a light sensing diode (protected by a quartz crystal) is inserted into the prechamber in place of the #1 glow plug. The diode registers the flash of light when the diesel fuel in the prechamber actually combusts and by comparing that signal and one from some kind of RPM sensor indexed to the crank, you can read the timing.
With the "pulse" method a piezio strain gauge element is tightly clamped to the #1 injector line and as the fuel is injected through the line it expands minutely. The piezio strain gauge registers this tiny amount of expansion and converts it to an electrical pulse that will trigger a standard inductive timing light.

NOW FOR THE REAL QUESTION... has anyone ever used (or tried to use) the luminescent type of meter for timing their Mercedes? Is there even any kind of indexing mark on the crank that could be used for the magnetic pickup? I just bought a Rotunda Tach & Time meter designed to be used for setting the timing on Ford 6.9 & 7.3 IDIs off of eBay.

I'll be using it to check the timing on my F250, of course, but I'm wondering if I can adapt it for use on my Mercedes.

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1984 300 Coupe TurboDiesel
Silver blue paint over navy blue interior
2nd owner & 2nd engine in an otherwise
99% original unmolested car
~210k miles on the clock

1986 Ford F250 4x4 Supercab
Charcoal & blue two tone paint over burgundy interior
Banks turbo, DRW, ZF-5 & SMF conversion
152k on the clock - actual mileage unknown