Ive heared of people doing this kind of thing to Minis before, but not Alfas,
Just been in my Alfa , after reading your post, I suppose the throw is a little long, but not so bad.
I imagine you could fit a GTV lever which would be shorter cos the seats lower in the GTV, however this would likely be very expensive. I think the lever is a solid bar with a thread on the end into which the nob fits, If you can get a tap and die set you can cut the lever and re-thread.
However, as I said just been in the car and it occurs to me that the gear lever is its length to be the optimum distance from the wheel. A shorter lever would be more annoying as it would be too far from the wheel making your driving experience worse.
Before attemping this I'd remove the nob which exends the shaft by about 4cm and improvise a temorary nob on the shaft which is lower with shaft right to top of nob then drive about a little to see how you like it.
I think you will find the increased gears to wheel distance more of an anoyance and decide to leave things as they are.