After about 400lbs/545Nm torque, stress loads are high enough to make the input shaft twist and push outwards towards the clutch. The case is then destroyed quickly.
VAP developed this robust solution which bolts from inside the bellhousing. (The transmission casing is not opened and no internal machine work is required.) Case/shaft flex is reduced and the gears are kept fully meshed together. (This saves the gear tips from snapping off under heavy torque and trashing the rest of the transmission). The tendency for bellhousing damage is eliminated. Since the part was installed on VAP's 800hp drag car, there have been zero failures. Protect yourself from big trouble and expense later.
Note: Minor case filing may be required due to slight variations in the casting process. Factory nut torque spec applies: 18 ft lbs plus 1/4 turn. See photos below.