I have a Hella ECE sealed beam conversion kit on my 300SD paired with Phillips Xtreme Vision 9003/H4 60/55w bulbs (bulbs were recommended by Daniel Stern and Candlepower Forums). My current setup is much better than the original sealed beams but there's room for improvement. The Hella ECE kit has issues with vertical jump between high and low beam, meaning if you aim the low beams where they're supposed to be, the high beam will be too high, and if you aim the high beams where they're supposed to be, the low beams will be too low. Of course, I didn't find out about this issue until after I'd installed them.

The lighting experts say Hella's Vision Plus SAE/DOT conversion kit is better in terms of focus and vertical jump between high and low beam. The Hella Vision Plus SAE/DOT kit isn't E-code, but today's SAE/DOT headlamps paired with quality bulbs like the Phillips Xtreme Vision or Tungsram Nightbreaker bulbs perform leaps and bounds better than sealed beams. The most important thing is aim. Properly aimed SAE/DOT lamps perform better than crappily aimed ECE lamps or properly aimed sealed beams.

Daniel Stern of Daniel Stern Lighting has recommended the Bosch ECE conversion kit as the best in terms of performance for the H6054 type unit used on the 81-85 W126. They're hard to find, though he can order some for you. For the 7" round headlights on the W123, he recommends Koito H4 conversion kits.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.