also- a really off-the-wall question here.... is it possible to put a top on an existing guitar?!
yes - i have done it a few times, but its a damn sight easier to make a body from scratch so probably wouldnt be an economically viable option.
As for ebony necks - pure black ebony is quite brittle, far too heavy and probably wouldnt sound that good unless it was with a dark sounding body would (although thas just opinion you understand). I would imagine the sound of the ebony would be far to bright with most body woods.
here are different kinds of ebony that might be more suitable, like macasser ebony (nice and stripey) but it would still need pairing with a suitable body wood to produce something usable.
I have made wenge and zebrano necks in the past and they worked well and felt great with an oil finish.. I also have a bloodwood neck blank waiting to be used which is red but very similar to ebony - so although i say ebony aint a great idea, i am still willing to experiment with it.
Also a note on the tone of limba/korina: It is sometimes easiest to say it sounds like mahoganybecause it is quite close but that doesnt mean its identical to mahogany. All the limba i have used has had a warmer and yet more articulate tone than mahogany bodied guitars i have made, i dont think it gets muddy sounding as easily as mahogany can.