Other indicators of Euro-ness are fabric seat upholstery (I've never seen or heard of a US W140 with fabric upholstery), flat face wheels (not offered on US W140s) and activated charcoal cabin filter (very infrequent option on a, please forgive me, low end S-class).

I would think a US spec 300SE harness would have very good to perfect fitment. You might have to content with a sensor or two out of place but it'll probably be an improvement over what you have now.

Let me know if you decide to switch wheels. I like how those wheels look on a W140.

Sixto
93 300SD