In theory, that shouldn't be too difficult. Put the cars side-by-side and do the swap. That way you'll know you have all the parts. I can't think of any differences between the years that would give you any major headaches. I haven't done an engine swap, though, so you should wait for responses from people who have done it before. (And I'm sure it's been done repeatedly). There are probably tricks that will make it go more smoothly than just diving in blindly.

Tim
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Tim Smith '85 745GLE M46 w/84k