Kind of a bad analogy to refer to the engine...
It's fairly easy to stick an electric motor into an IC car (there was a project a few years ago for an electric land rover, unbolt engine and gearbox, drop in electric gubbins).
Brakes would be just as easy, only complicated if you want regenerative braking.
The air-conditioning would actually be the hardest part to exchange
So, you could make it a better analogy by swapping it around.
Instead of making the car fit the engine, you have to make the ancillaries fit.
The ancillaries are the specific techniques btw - the big stuff is easy, it's the little stuff that make it difficult when you add them up.