Engine in an 1984 318is

My brother recently killed the engine in my '84 318is due to a lack of oil. Although I haven't taken the engine apart to see what exactly is dead, I am considering swapping the engine since it is much easier than having engine work done. Which engines will bolt in to the '84 chassis? Thanks ahead for any help.

I would go for an M50 motor . . . I6 2.5L

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