Many members of the various Mecedes forums say the updated to Pencile type glow plugs is much better and if one goes bad the others can still work.
Most recommend only buying the Glow Plugs and making your own Jumper Wires.
I know from what I have read that the 1976 Glow Plug relays will not work with them because it has a Max of 50 amps.
If your present Relay uses an 80 amp Fuse there is a good chance it could work.
On the systems with no Relay where you pull a knob out I believe just using the updated Glow Plugs is OK.
See our DIY sections for more details:
DIY Repair Links
http://www.peachparts.com/shopforum/diy-links-parts-category/
http://www.peachparts.com/Wikka/DoItYourSelf