http://www.ferrarichat.com/forum/ferrari-parts-collectibles/522754-two-599-engines.html A rare find!! Erik
I don't that is something you would do unless you have "special interest" for being many sleepless nights in the workshop.... But it might be possible.
An early one (156938 or earlier) with Motronic 7.1.1 might be a pretty easy swap. Or a late one into a late 612 with 7.3.2. Would still be a hassle matching the clutches, etc, but doable with enough money.