It's been my experience that the only way to get the correct original tii AL-40X is to buy a rebuilt used one. All of the new ones that I've seen come from Bosch are the ones with the shorter boss and the adapter. The rebuilt originals go for over double what you'll pay for a Bosch rebuilt with the adapter. BnR offers a custom higher output model (85 AMP) with internal regulator that they (BnR) custom machine the boss to fit the tii. I haven't tried one because I didn't want to ditch the external regulator.
http://www.ebay.com/itm/BMW-2002-TII-Alternator-85-AMP-Drop-in-Bosch-Built-in-2002-Tii-Generator-/350997786226?pt=Motors_Car_Truck_Parts_Accessories&hash=item51b9192e72&vxp=mtr
The pulleys that come on the BnR rebuilt alternators are too small, so unless you want to use a smaller fan belt, you will have to swap your original pulley and key onto the BnR rebuilt. They also don't install a key in the pulley, so you have to use an air wrench to remove the nut on the pulley because it will spin because there's no key to keep the shaft from spinning. At least that has been my experience.
John
Both of my tiis '73 & '74 originally came with the same wider boss Al-40X alternator.