I know of someone who was doing a 240D into a 300, and If you use the search feature of this site you may find that I once posted a link to a site showing a 300SD engine into a former 240D car.
So this is a very doable swap, but my recommendation would be that you carefully consider the cost in time and $ before you get too deep. If you are a determined person who can do most of the work yourself...I say "go for it !" If you have to have a shop do it for you, I don't think it would be worth it.

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Diesel-guy