I already know the TR3650 will have to go and be replaced with a T56, but what about the rear end? Can it take around 600HP and 550Lb/ft torque? No drag racing on slicks or drag radials, mostly track so it wouldn't be shocked by hard launches. I'm guessing at least the axles would need to be replaced. I'm also looking at a Torsen Differential, which should take the power considering it's used on racecars.

I'm scouring Ebay for a used '13 to'14 GT500 rear end with 3:73 gears and the Torsen already istalled but no luck so far. There used to be this one available from Ford, but it seems to be out of production: Part # M-4001-SVT373

 

Primary difference between the standard gt and the GT500 is that the GT500 uses carbon fiber discs in the LSD and 31 spline axles instead of 28.

You can just buy the FRPP LSD with carbon fiber discs and just replace your existing one.

Complete LSD with Carbon Fiber discs
http://www.americanmuscle.com/ford-3...arbondisc.html

or just an LSD rebuild to upgrade to Carbon Fiber discs.
http://www.americanmuscle.com/ford-88-traclok-kit.html

31 Spline axles is required if you get the complete LSD.
http://www.americanmuscle.com/srperf...xles-0514.html

And, I think you'll be find with that power output as long as you don't put drag radials on the rear but, you may find your rear will wear out faster unless you at least get the Carbon fiber upgrade to the LSD discs.

 

I thought starting with our generation, all GTs had 31 spline axles?

 

Derp, you are correct!
http://www.americanmuscle.com/tech-a...le-shafts.html

So, even easier, just swap the existing LSD unit with a complete one that already has the Carbon Fiber discs...

 

Your axles should be fine but your discs, carbon fiber or not will wear out at that level of power. I'd get a tru-trac and not worry about it again. And replace the axles seals while you're in there.