I'm looking around for options. I can't find a good answer. Do any GS 400s come with an LSD? Or is the only option Aristo/supra Turbo Auto rear end swap (Unavailable) Or Os Giken LSD (Expensive AF)?

 

There was no factory LSD for this model.

 

The only option is swapping in a torsen diff from an Aristo/Supra automatic or having your diff rebuilt with a clutch type diff. There are other options other than OS Giken. Tomei makes one and Kaaz also makes one. Still expensive but much cheaper than OS Giken