The entire drivetrain, every moving part from the clutch bell to the wheel hexes will need to be upgraded. I'll try to list for you, pipe in anyone if I forgot something...

Clutch bell, spur gear, transmission output drivecups, driveshafts, differential spurs, spider gears, differential cases, diff covers would be a good idea too, diff outdrives, front and rear axles (dogbones), wheel hexes. You probably don't need to do all of this at the same time, start with a few and see how the rest hold up, replace them as you destroy them would be my plan.