Yeah, go for the 3.9. You've got the same set up as me, and my 3.9 is spot on I reckon. I agree with blind elk, that being a rally diff. You'd have no problem selling it on Bridibella ( rall site). I dynoed my l28 the other day, made 142@ the wheels. The tune was average apparantley,running way to rich. I have 72 grind coming from POWER PLAY which should be in in a week, current grind 68. Then I'm getting it tuned on a dyno, rather than by ear.