There's so such thing as an 86 SD. W126 dashes should all swap. Keep in mind that early build 1981 models had the CC sensor in the dash, so consider that if you look at another dash.

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'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.