SC Trac-Loc's
The Trak-Loks in SC are all Meduim Duty (MD). I've shreaded 2 OEM MD Track-Loks in my '89 XR-7! They might work fine behind a modded 4.6, but they can't take the tq of an SC! At the very least, you should rebuild a MD Trac-Lok to HD specs. I believe that involves adding 2 clutch disks. Don't know if that's per side, or total.
If you want a differential that you'll never have to reaplce, get the FRPP Torsen! They're gear-on-gear, so there's nothing to wear out. They are also smooth as silk.
I have an Auburn Cone in my car now, & it transferrs tq very oddly. Also, I can feel BOTH cones slip about 1/2 revolution when I get on it.
68COUGAR