Dunc is right on the money of course; it can all be done, and it's all 'bolt-on' stuff (no welding/cutting to the structure). You should probably still consider/check out the insurance ramifications though.
As for the choice of buying an Alfa Romeo 155 Q4 - well, what can I say

Of course it's going to be a lot 'more' of a car than the Uno - it was undoubtedly more expensive - whether you like the styling or not may be a deciding factor, and there's also the thought that the 155 Q4 will be an 'ordinary' 155 Q4, whereas your special hand-assembled Uno Turbo will always be a 'special'.
In the grand scheme of things, the 155 is still a fairly old car - the Uno is turning into a classic! In terms of 'gizmos for the money', comfort, speed etc. newer cars will usually outstrip the Uno, but the fact is that neither car is exactly 'new', so you may as well base your decision on more personal criteria: which do you feel would be more 'yours'?
-Alex