so i am buying an 85 gsl-se rear end to put in my gsl... what do i need to do this besides a different pair of rims for the bolt pattern? is it a straight up swap?

 

Yes, it is a bolt in deal when done as an assembly. Meaning you need the calipers, rotors and axles. The housing is the same as the one currently in your car.

-billy

 

ok because it is the whole setup calipers and all... would trailing arms and mounts work from a 83 casing or no?

 

There is a slight difference in lower arm length for the S3, but you will be fine. You will need the right and left hand rear brake cables for the disc brakes. If they don't come with the package, Black Dragon sells them. If you already have disc brakes, then you're good to go.