If you are working on a 105 type car the simple solution is to just swap out a 115 complete diff assembly, as all the mounting bolts & hardware are similar and in the same location on the axles.
BUT, for you few enquiring minds: 
The 115 LSD unit can be modified to fit into all the other rear end configurations. The 750, 101, and 105 series.
I won`t tell you how but there are pics at :
http://www.alfabb.com/bb/forums/giul...ta-spider.html
It requires having the right machinist, metalurgist, and fabricator
