I actually have a mustang I did the IRS swap on. Its not the halfshafts that make the rear end not able to handle power. It is actually the bushings in the rear that make the halfshafts break. What happens is that the stick rubber mounts allow alot of movement of the diff. This causes the axle joint angle to severely increase causing alot of strain on the joints during hard launches. The actual axles can handle alot of power. Ive seen people put 1000hp onto those stock axles after replacing the bushings without an issue. However, I have seen people put in those "1000 HP" halfshafts and break them with 500hp. The full tilt boogie kit is your best bet. the mms setup comes with alot of urethane bushings which wear out easily under large stresses. Also, it may seem hard to grasp, but the hard delrin bushings in the ftbr kit actually give a better ride the the softer rubber bushings that come stock in the cobra IRS. It is because it eliminates binding which eliminates the rebound the rubber bushings produce. Also, this will increase handling tremendously as it will remove all the play in the setup. I also just bought an S30. I am converting it to a double wishbone setup aswell, but it is completely custom. I am using z32 components and making a cradle to hold the diff and lower control arms. I am then mounting the upper control arms to the frame rails that are already there. Ill make a thread later on this week when I hope to finish up alot of the fabrication.