I believe that piece is spot welded in with large spot welds. If you want a factory appearance then drill the spots out and weld in the new piece using plug welds to replicate the spots. You can also stitch weld the box on the outer perimeter. Either way weld penetration should be ample, just be sure to remove interior from the weld area due to heat transfer. If you take precise measurements of where the current box is then you should be fine. I am sure you have a small amount of slop in positioning but I wouldn't get away from the measurements too far. Hope this helps.
---------- Post added at 07:27 PM ---------- Previous post was at 07:22 PM ----------
Originally Posted by WhiteCobra94
What's the Max horsepower and torque the stock torque box can handle?
I would guess that this depends on if you are drag racing or just a spirited street run from time to time. I have seen 400 RWHP Foxes running unreinforced battle boxes. I probably would not do that as the constant hard take offs that tend to come with high horsepower would take their toll. I think if you are pushing over 300 at the wheels then it's time to think about reinforcements as well as driveline upgrades.