I don't see a need for anything aftermarket here. Use the older spring, new toyota clutches and shim the diff testing the breakaway torque as I described in my supraforums thread. ~80 ft/lbs is perfect for street strip and will handle a lot of power. Use a standard 75-90 gear oil. My diff has been holding up great, I drive my car to and from the track (and race it a lot), the car put down 680 at the wheels,runs 295 50 16 drag radial which is almost 28" tall and weighs 3715. You could achieve more breakaway torque shimming the diff more on this spring, but I didn't see a point in driving around on a pretty much locked diff.
There is nothing left to do on these diffs, they work great. The ring and pinion on the other hand is too small to hit hard.
I have pics of the two different spings next to each other I'll post up shortly.