This guy is selling a part to his 370z differential. Would this be an easy way of upgrading my 3.5 gears to 3.69FD gears? Or would this part just change my diff from open to lsd, which i already have lsd. Its going for a $140 Is this a hard part to swap without taking it to a shop?
Id appreciate some answers!

Upgrade your open (2 pin) R200 differential for LESS $$$!
Nissan part number: 38420-2C500 - viscous assembly for differential
This part is over $600 at your local Nissan stealership.
0 miles on it! Removed from a brand new R200V.
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That is the differential. Will not change the final drive