You can interchange the lights and turn signals. But, are the lights on the 89 US spec or Euros? If they're US spec, I wouldn't bother with them. I'd either get Euros, or buy one of those sealed beam to E-code H4 conversion kits. With the 86-91 US spec lights, you have a poor lens pattern, same with the 81-85 US spec lights. EXCEPT, with the 81-85 lights, you can simply swap a 7" hi/low beam unit in that has the good E-code lens pattern and H4 bulbs. With the 86-91 lights, no matter what kind of bulb you put in the hi/low assemblies, you still have the sucky lens pattern because you simply replace bulbs, and not the whole unit including the lens as with the earlier models. The seats from the SE should fit the SD too.

__________________
'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.