915 Gearbox Differential part numbers help
 

A good friend of mine has a 3.2 1984 targa with a 915 Box and very oddly, it needs a differential.

Does anyone know the difference between the two part numbers below, Porsche haven't even been able to answer this so I'm praying someone here might, they are both Diffs:

93033221201
91533221200

I would guess that the one starting with 930 would be for a Turbo but apparently this is not the case.

Thanks in advance. Nick.