hi did you sort the problem out, i have the same problem and i was going to tackle it myself and then read your thread and i am now having second thoughts!!
As mentioned above, be careful. This is ordinarily an easy job (apparently), but in my experience, i found once removed, there was not enough room to put the parts back in which lead me to taking off parts i shouldn't have. The gear selector shaft wouldn't go back in as my nylon bushes it sat within had expanded too far.
After my last post i had worked out what i had done, i repositioned the selector and regained all gears, but my selector was still stiff. i booked it in at alfa dealership, £60 later and i can't believe how beautiful the gear change actually is, it was like having a completely different car back from them.
It goes through the gears now like a GTV, the torque from one to the next is amazing, no losing time between changes like before.
I am unsure if there was less room to work with the 2.4 JTD engine bay and maybe thats why i ran into problems, but i would personally recommend spending the £60 with alfa to get this job done, if nothing else, for peace of mind
hope that helps