Rear Diff HELP

[JEVANS25]

Hello, 
I need to buy a new (used) rear diff for my '04 1.8t BEX 190 
I was given the diff code FUB by the garage and have found one with matching FUB 

Will any diff with FUB code be a match?
I saw some comments regarding making sure that the gear ratios match but does the matching code ensure this?

The used diff i am looking at came from a 2005 A6 3.2 FSI which is why i am cautious but do they just share some parts?
Hope y'all can help

Cheers, 
James