Mel:
The frames do look very similar, but, at some point, I had done some measuring for the sake of argument, and IIRC, the F250 HD frame was about 1.5-2" taller than a 150 unit in most places, the C was wider, and the thickness is about double. Now, a BKO may be it's own animal.
FWIW, the 460 and diesel trucks(all over 8500) use the exact same frame, and the later 96/7 5.8 over 8500 trucks do also.
As for that 7.3 mating to a C6, you need the diesel C6 and flexplate to suit, the engine adapter plate is the same auto/stick. As for the E4OD, you could run that with a divorced transfer case, but, you're adding a bunch of electrical complication that is really unneeded. I'd stick to a C6, or preferably a manual of the ZF persuasion.