JSA. i have a track escort cosworth i am building up and have a supra LSD rear diff to go in it. i have also got a standard supra diff or JZ90 or something with a supposed 3.9 to 1 ratio. it seem you are quite knowledgable in these diffs would the 3.9 ratio crown and pinion fit iob the LSd diff this has a 4.56 i think in it.