They are DIFFERENT but can be interchanged with some parts swap. Most do this for the possibility of using a 1750 LS differential, more complicated. You maintain your Giulia 1600 tubes, backing plates outer bearings and so on. HOWEVER the later 1750 and 2L LS centers require you to slice the inner flanges from the 1600 and 2L to narrow the Giulia tubes as the 2L center is wider than the 1600. Jack Beck used to make these. Richard Jemison Alfar7 on the BB does these now. Contact Richard for details. I admit to NOT being an Alfa Gearologist. RJ built my last 2L LS 4:56 axle used in my '65 spider and it has given me no issues.
As Gordon notes, the two rear axle assemblies are quite different. Was that your question, or were you asking about the internal parts of the axle assembly (e.g., just the differential, AKA "the diff")?
Alfisti have installed 105 rear axle assemblies in their 750/101 chassis by cutting off the 105 trailing arm brackets and welding on 750/101 spring perches & trailing arm brackets. But you still need to deal with the triangle that locates to the center of the axle. A company called "Z Engineering" used to make a conversion kit for this, but I don't know if anyone offers those parts today.