Hmmm,
The 126 ended production in 1991 well before the invention of xenon headlamp technology...... To be quite honest I think it would look funny on a car that old to have xenon headlights...... Are you doing this for an appearance upgrade or just for additional light? You would be amazed at how much light the european lamps put out on their own with standard halogen bulbs. Additionally without an automatic leveling system you may be blinding other drivers. A head on crash with a night blind blue haired old woman in a Lincoln Townhouse would easily outweigh any visual benefit.
I have factory installed Euro lamps on my 126.
http://beostar.paunix.org/newmbzpics
I have thought about xenons on my 140 but will probably hold off because I would want the factory components rather than go aftermarket. While the headlamp units look the same on the outside they are somewhat different on the inside as I think there is a leveling system on the xenon headlamp.