WOW old thread.
Anyway, yes I installed (successfully and easily) the later afterglow system into my 300SDL.
You basically need the later plug relay, different cylinder head sender with two pins (other pin is for GP relay), few plastic connectors, solder, some quality wire, and a bit of time.
I believe Bosch only makes the afterglow style glowplugs now (80006 or something is the PN) and you would need those if you do not have them. GP life is shortened obviously, but not to a year or two. I have one or two plugs out since my install which was probably in 2005 or 2006.