If you piece the DS together from the two cars it should work. I would send the DS unit out for balancing. Here that costs about 50$. You have to have the DS in good shape though. All bushings,center bearing, U joint, and flex discs must be in good shape for the balancing to work. To cut my DS was only 200$. If all parts must be renewed for balancing your looking at around 400$. I would make sure everything is up to snuff before sending it in. If you send it out without renewing things, they will have you for some$$ if things are in need of replacement.
It went like this for me.
Brought my DS in for shortening. was quoted at 250$ for cut and balance. Of course my judgement on the shape of the DS was not correct. It was fine while driving before. Once it was out it needed a complete rebuild. He would not balance it without. Everything listed above was replaced. The cost was around $400 including flex discs. so Ended up Paying 675 or so for a completely rebuilt and shortened DS. OUch! Had no choice.

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Chris
84 280sl
82 300d euro