My buddy has a GSR and bought a quife lsd... he isnt going to use it anymore and is selling it. I would be able to use this on my Si tranny with no modification or problems right?

 

you will need to use a ring gear from a GSR, the SI bolt pattern is smaller even though its the same ratio.
Also, you can go with either GSR or SI diff bearings, I prefer the GSR since the're tapered, but the SIs are fine if you don't want to buy new GSR bearings and races.

 

Thanks for the info. I can pick it up for $600. They go for new around 850. Would it wind up being cheaper for me just to pick one up made for my car?

 

You can easily sell that one for $750 if its new, and I can get you another one for around $800 shipped, but $600 is a damn good price, and you can probably find a good used ring gear here on HT for $50 or less, so it might still be a good idea to go that route.