Hello, everyone!

Recently purchased 1990 300E that was custom lowered by PO. Car is super good cosmetical condition with just over 100K on the engine. Engine and tranny runs strong, but i there is a little noise from the rear end (especially when i am accelerating) and small vibration between 60-70mph from the drive shaft. I have not had a chance to check my flex disks yet, but i am trying to be prepared for diff swap. I have a chance to get rear differential and speedo from 94 e320 Wagon with 100K on it.
So my question is as it says in the title: Can i swap differential from 94 E320 Wan to 90 300E? I believe gears ratio is different, so what changes in performance i will face?
I will also post a picture of this car - so, if anyone knows more about history of this car, please, let me know. PO was not very cooperative.... But price was very tempting, so i can't pass on it. Ran auto check - all good and clear. This car spend most of it life in Nevada, but now in TX.

Thanks in advance!

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1987 300D Turbo 170K (sold)
1990 300E
1992 300D 2.5 Turbo
2003 Audi A6 4.2