The weakest part of the geabox is pretty much the standard open diff. Replace that with a Quaife and you will have a very hard time trying to break the thing, unless you are into crunching through gear changes

The Quaife is rated to 700bhp going off previous applications.
The Fireballed car runs a stock Getrag gearbox with a stock LSD on the drag strip no problems. 500+ bhp and more torque than will ever be possible to produce with the supercharger alone.
Cheers,
Henry