yeah I suppose it's always easier to start with a car that runs.
Nothing to stop you swapping the engine yourself if you know the new one is ok, it's not that hard to do a like for like change later on... or are you selling the black one?
If you were wanting to be really drastic you could swap over all the body panels from the black car and just get the roof wrapped black
__________________
------------------------------
------------------------------
__________________
------------------------------
------------------------------
|