Can I put an 86-87 TII rear differential in a 90 GTU, and will my car be better because of it?

 

i'm not sure if it'll fit (i dont see why not tho) but you'll only notice a difference under hard driving (corners moreover..) and launches.

otherwise you wont even notice it

 

you would have to change out the half shaft

 

the drive shaft won't bolt up, you need to swap the turbo tranny and drive shaft at the same time.

 

Scott and Icemark are right. The T2 diff will only match up with a T2 driveshaft and T2 halfshafts. The T2 driveshaft is a different length and will not mate up with the NA tranny, so you need a T2 tranny.

And in the end, you're still not going to beat your T2 buddy with those parts

PaulC