[Mike C]

You can beef it up, but a car 12 bolt is stronger. If you really put the power out you are talking about and hook it up at 4000#, you will break it. A lot. 12 bolts don't do well with big tires and lots of traction. At last count I think 6 was how many I had broken in my Jimmy. I'd be looking for a Dana 60 and have new ends put on for semi float 5 lug axles. Especially if you have a coil spring truck. Much cheaper than doing a custom 9".