Texasdoc Tom you are right about the amount of torque that your trans can handle. The other thing is was the bellhousing centered on the block and checked for out of round? What bellhousing are you using? I hope it's an aftermarket one. Quicktime, Lakewood,( the worst for being off center) for even the stock setup needs to be checked. After this is done, you need a new front bearing and seal for the input if you stay with the T5 trans.
I am not a big fan of these trannies and would tell you to lok at the Richmond super street 5 speed trans with OD. The design is stronger, bolts right in and can use the orignial looking shifter and handle in the car. May have to center it on the tunnel or even relocate. This trans cost more but has only 2 main shafts and not 3 or 4 to supply power to and wear out with abusive driving. I ran a 6spd richmond for 7 years without a problem after junking the centerforce clutch. This trans has a 450/450 rating but is 1" longer in the mounting location and 1st gear is not used. Find a trans with a 2.80 or less first gear. Because of the power and weight of the car, you don't need anything higher unless you are plowing a field or pulling out stumps.
I swapped to a G-Force 5 spd because of racing and hard abuse. Also uped the power to 500/600 and the 6spd would handle it but not the abuse level.
Take the nose off the trans and get a new bearing input housing, bearing and seal if it don't come complete and swap over. This will get you running again.Drive easy and enjoy. Rick L.