[RICK LAKE]

needtobuy LH 600 hp is not out of the question but things like having enough fuel supply, strong fuel pump, running a careful timing setup. You also should look into a Snow water/methanol injection system to pervent and cool the combustion temps. EGT gauge would also be a good idea.
A good blow off valve to help control boost. You didn't say which Paxton blower you are running, If it's a ball bearing setup, this is a safe one to stop blower pressure from banging the impellor when going from full boost to closing the throttle plate. The pressure has no where to go and bangs the blower. Ball bearing blower are less effected than gear drivin ones. You are going to need about 9-10 psi for 600 hp or torque. The stock injectors will be running about a 90% duty cycle, This is hard on them. Should go to the 42pound injectors with the same ohm range as what is in the car and have the motor recalibrated on a chassic dyno. Hi test gas and booster wouldn't hurt either. Make sure the O2 sensors are not effected by lead additives.
Last note, run the motor a little soft on the A/F ratio and keep the timing down to 2 degrees less with each pound of boost added to the motor.
I wouldn't keep pounding on this motor, roll on and off the gas. You may want to look at the exhaust system first for restriction of the motor if you are running side pipes with mufflers inside. This can cause you 10-60 HP alone. Good luck This should get you in the high 500's. Trans should be OK as long as no 3,000 rpm clutch drops to the drive train on soft tires. Rick L. Ps I don't know what kind of work was done to the Jag rearend but they are rated at 450/450 with 27 spline axles. CWI sells a 30 spline kit for the 600/600 club. I have seen 27 and 19 spline axles twist with good power and sticky tires. That carrier is only a Dana 44. Adding a support carrier cover to help control the caps for the rearend is also a good idea. LWP sells them. Been runing one for 13 years, no failures with the 30 spline setup and a locker inside. Rick