i don't pretend to know a lot about doing serious mods to vehicles, so take this for what it is worth: What about swapping out the rearend from a different vehicle with independant rear suspension (vipers, corvette, and cobras) all come to mind. You end up with a rear end capable of supporting high horsepower/torque applications, is limited slip and has lots of gear options.
Spend the money to have the housing tweaked/reconfigured to work in a crossfire, rather than spend cash to build crossfire specific gears and limited slip.

To me it seems making a housing work would be easier than fitting custom gears - maybe I have watched one to many muscle car buildup shows on the weekend.

Just a thought.

Cheers,
KrzyFast