I know this has been talked about many a time, but I can't seem to find the answer to my specific question. I have an 89 GXL and I want a LSD for it. What is the easiest way to go, and what is the cheapest way to go? And what would you do?

 

get a lsd from a s4 gxl ,direct bolt in, dont need to change anything.

 

Would I need the whole rear end? Or just the gears? and is that the clutch type?

 

Just the pumpkin.

 

As stated above swapping the pumpkin as a unit from a S4 with LSD would be easiest. Or if you could find a '89-90GTUs in the boneyard.Also some late model Miatas(not sure which ones other than '94+ but a search should turn it up) had a torsen LSD that will swap in but it's a bit of work. Here a link to the Miata install.
https://www.rx7club.com/forum/showthread.php?t=229115

 

just grab the whole pumpkin from a s4, IE: disconnect drive shaft, disconnect half shafts, undo mounts, and reverse w/ the new one and vuola, lots of dorifuto fun!

 

If I find one in a junk yard is it most likely going to need to be rebuilt? Do s4's have the clutch type? what about s5's?

 

s4 is clutch type, s5 is viscous ( correct me if I am wrong ) if you try to use a s5 one you will need it from a GTUs = pretty ****** rare,
you could use one from a TII but you would have to swap out the drive train or some **** like that,
I honestly loved the s4 lsd, I say find someone who is parting out a car ( so its not too old )
if you get it from a junk yard ( I wouldn't) u would prolly need to rebiuld it.