There is no doubt that most things 'can' be done ,I'm just sort of left asking 'why'?
Personally, if I were to invest that much time and effort in creating a 9000 engined 99 I rather think that I would have gone the tenth tenth and put the engine in the middle and have it drive the rear wheels.
Certainly wouldn't hurt the handling. Perhaps wouldn't do much for passenger comfort though.
Like for like, there's only 20 kgs between the 99 and 900. It's the fact that the latter tends to get loaded to the hilt with stuff like power steering, electric sunroof and windows, and that the 99 wasn't ever built with the 16vT motor that we think of the 99 as much lighter...