Can an 89-90 turbo 2 limited slip differential work on an 87 n/a without any modifications? If there are modifications needed what are they.

 

everything will need to be changed. If you run a t2 diff you need the t2 half shafts, and have to come up with a drive shaft. The NA shaft wont bolt up to a t2 diff, and a t2 driveshaft wont plug into a NA trans. So you either are going to swap the trans, clutch, ext, or get a drive shaft custom built.

 

How about a 88 NA differential, would it fit on a 89+ NA Rear?

 

Swapping N/A to N/A = yep

Lots of guys get the S4 clutch pack LSD's from the GXL's for their S5's.

 

Clutch-types wear out, so what do people do to "freshen up" their clutch pack LSD?

 

rebuild them.... the clutch packs and tensioner springs are readily availible