There is a whole 3 page article on this topic in the July/August 2000 issue of The Star on page 76. It covers all the parts you will need as well as wiring instuctions and set up for the manual adjustment switch you can add.
The article is on the pre 94 models and they say it is the same for the 300E, 300CE and 300TE. They replaced the stock lights with european 500E headlights.
1995 E420 - retired
1986 420SEL - retired