Good early morning fellow Subaru enthusiast I have a quick question I got a 1984 Subaru Brat runs great and that I have driven before but somebody took the driver side rear half shaft and CV axle assembly out because the bearing disintegrated and was pretty much useless and I'm wondering that if my 85 Subaru GL half shaft assembly will fit on an 84 brat and also how much of the parts are Universal going from car to car

Some parts do interchange but the axles don't. The ea82 axles are longer than ea81 (brat).

Very few drivetrain parts interchange directly. 

GD

Instead of changing out just the axles can i take the whole hub and half shaft assembly where it bolts on to the unibody and rear strut from an ea82 and swap it over to a brat? If that were to work id probably have to swap both sides. But is that a possibly?

No. Subframe swap required = custom work. New shaft cheaper and easier. 

Cheers 

Bennie

No. Nothing will directly swap. They are entirely different drivetrains. The whole car is wider. 

GD