Your problem may be simpler than you think, and cheaper than retrofitting to the new style plugs. Take off all the wires between the glow plugs and at each end (even the end that grounds to the engine itself) and give them a good cleaning with a wire brush until they are nice and shiney. Do the same with the glow plugs themselves. Clean any metal connection that makes electrical contact. Then reattach everything and give it a try.

Recently bought a car that would not start. Tried everything, including ether. Wouldn't even hit. Turned out one of the connections on the glow plugs had corrosion and excessive resistance. Once the connections were cleaned, the engine started right up. I would never have thought that could make so much of a difference, but it did.