You will also need a clutch pedal, new brake pedal, new engine management
(probably), alterations to the transmission tunnel etc. etc.
The chances are it will not work, and I can't see how the cost involved can
be worth it on such an old car.
There were a [very] few E32 735i / 735iL (for chauffeur driven) around with
manual boxes from introduction in the late 80's to ~1992 - look for one of
those. The current E63 645i has an optional 6 speed box, and there are a
few of those.
In the 1980's I had a couple of E23 735i manuals, and they were a sparkling
drive out of town, but hard work within it.
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