I have found a supplier for 4/1 and 4/4 diffs for sierra units if anyone is interested ,its a company called Kamdifferentials
See website.
I could be wrong, but arn't those the ones that raceline sell ? linky
Raceline have none available ,told me no supply available. Understand Quaife have aquired interest in Kamdiffs. I am putting 60g direct top sequential in Indy R with duratec and need top speed 120mph