B787 - a different beast, a different beauty
@No_Fly_Zone has it down pretty accurately, just to add another 2 bits worth:
The cinchiest conversion IMHO has been the one from B744 to the B777.
B777 to B787 not so simple, the differences require a different mindset too. Keep kicking yourself when asked by an old fashioned B744 skipper sitting in the sim, half question, half statement, "so the APU can be started at F430 and is it's bleed only usable till 22,000 ft, or throughout the envelope?" and for that split moment, you puzzle over it, trying to figure how it works, yet vaguely resentful because you know the question isn't 'legit', you even start thinking - why did i never think about that??, then sudden relief . . . . "Oh, Captain, we don't have/use bleed air on this airplane, and the engines start using electric starter-generators. We do not have a X-Bleed Start, we have a X-Start.
"why am I seeing the amber alert HYD L + C + R before engine start, all pumps are 'on' or 'auto(= enabled)' " - so then . . . you ninny, brakes are electric, and there's no body gear or main gear steering! (it's sophisticated, and small)
The B787 IRU's can be aligned inflight - sweet? Once on the Triple I'd berated an ex-naval pilot for blaspheming, by even suggesting this. That too on his Soviet built heavy metal contra-rotating multi crewed Godzilla shaming monster bird. Clearly, it was his ineptitude at back-answering authority and my good luck that my statement prevailed.