I converted a 190D to the new glow plugs. It worked great. You should install a short piece if copper wire in the glow plug indicator in the dash board to eliminate the resistance of the glow indicater wire. This will allow the glow plugs to get hotter.
All the glow plugs should be the new style.
You can take the glow plugs out of the engine
to see if they are getting hot enough: they should all glow red hot. Each one must be grounded to the engine properly to do this test.
P E H