I had my 84 300SD fitted with a 85 SD tranny it fits perfectly on the 84 the only problem are the electrical connectors they are completely different but some tinkering will solve that , at worst you will lose the electric passing gear if you don't hook up the right wires oh and if you hook up the wrong wires the passing gear will not work but won't burn anything it just wont work until the wires are corrected.

Good luck

twr

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2000 430 ML
2005 S500
87 300 D
61 300 restoring