You can run true duals as long as you run a balance pipe, either an H-pipe or an X-pipe will work. At that point they would balance out and sound good. Now, assuming you we're going to run 2.5" dual piping into the stacks, the other option would be to consider using a Y-pipe. Running 2.5" from the manifolds into a good quality manufactured Y-pipe from someone like Flowmaster or Magnaflow, and into a single 3.0" system will provide the pressure balance to the exhaust you need to get even flow from all the cylinders.
Another reason I bring the Y-pipe up is about 20 years ago when I was still building my knowledge base of things automotive, I did some rather extensive testing of exhaust systems for trucks used for towing. I fouls that with stock manifolds 2.25" or 2.5", whichever fit the manifold best, merged into a good Y-pipe and run through a single 3.0" system produced the best torque. With headers the best was 2.5" into a Y-pipe and out 3.5" piping. Your 7.3IDI won't flow anywhere near the air volume of a 460 Ford or 454 Chevrolet, so the 3.0" would truly be best.
And at the same time, any single system will make make adapting an over the counter dual stack kit a whole lot easier.
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The Current Truck (Oct-2013 to Present):
1999 (Early) F-350 Lariat, CCLB, SRW, Black/Tan
7.3L Powerstroke, 4R100, 4x4, 3.73, 37x13.50-18s, '05 Axle Swap, 6" Fabtech lift, GTP38 "D66" turbo upgrade, SCT 4-position chip with custom tuning by me, Straight Piped 4" down pipe through 5" dual stacks, N-Fab full length triple steps, Pro-Tech cab guard and tool box, louvered 5th wheel gate, Hella 500 Fog and Driving lamps, much more to come...
The one I'll miss, (Mar-2009 to Jan-2014):
2000 Excursion XLT 4x4
6.8L V-10, 4R100, 4.30, 285/75-18, 271whp / 388wtq
The one I won't, (Jul-2005 to Sep-2012):
2005 F-350 XLT, CCLB, SRW, 4x4 FX4
6.0L PSD, ZF-6S650, 3.73, 35x12.5-18, 4.5" Lift