Re: Very bad vibrations....
In response to question one, yes, both driveshafts are the same, it's only the length of the inner cup thingy that differs.
That cup isn't part of the driveshaft, unless you send yours off to be re-conned with the cup too, but that will need to be priced up seperately, but shouldn't be much money.
The 3 prong thingy is part of the driveshaft, but the cup isn't. It's a seperate item and costs around £80 or so for a re-con one through Alfa. Car parts direct should be able to do this for you cheaper though I'd suggest. There isn't a part number for the 20v type driveshaft at driveshaft direct as there are 6 or so to chose from, all with different part numbers which don't relate to the Alfa part numbers, so unless you send your one off to them(they'll pick up with their courier next day), I wouldn't bother getting one sent to you as there is a 1 in 6 chance it'll be wrong. If it were me again, I'd take off the driveshaft and inner cup complete and take a photo, along with the picture from eper, e:mail them the pictures and ring up to arrange the collection and re-con with a fixed price. They can turn them aroun in 2 or 3 days back to you again.
Are you going to be fitting yourself or will the garage be doing it?! Good luck with it, let me know how you got on.