Hotfingrs Jack If you talk to Mark Willaims they will set you up with a set of axles that you will not break. I don't know what IRS you are using but if you go to a Quickchange or a Franklin, good for 800/750 HP and Torque. Endless gears changes too. The older vette rears are now 7.50 legal in NHRA with a custom 12 bolt setup inside the case. Have heard there is no problems but needs the stub shafts checked every 50 runs for twisting. Jag rearend is good to 600 hp + after some work with cap girdle and 30 spline axles.
Hope Dave puts a better rollbar or cage in the car if he is going to do this time and speed.
Rick L