There is no such thing as a "reputable" (or functional for that matter) HID conversion except to replace entire headlight unit for one designed from the start for HID.
This doesn't exist for W140.
http://www.danielsternlighting.com/tech/bulbs/Hid/conversions/conversions.html
Look into brighter halogen bulbs.
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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles
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