Honestly, id swap a 4r into a truck at 500hp. If you tow a lot and like the downshifting, a 5r is nice. altho with some careful tuning a 4r could be made to do similar.
After driving a truck that went from 5r to 4r, its hands down better. spools faster, burns the tires better, will shift and lock WHEREVER you want it to, and less smoke out the tail pipe. I know it goes against conventional wisdom that the 6.0 would run better by losing a gear, but theres more than meets the eye. A lot of it has to do with the converter used as well. From what weve seen, a 4r is more reliable over 500-600 hp than a 5r is, on a large scale. Some trucks will hold big power with a 5r for years, others eat them like candy. And this is even with propper tuning.
Also, isn't craigs fastest pass on the 4r? I might be mistaken but seems like I remember that for some reason. maybe one of the mpd guys will chime in and set it straight.
Once you ride in a truck with a BTS 4r, you wont want anything else.
On edit, I almost forgot to answer the OPs question. Youll use a modular (gas) 4r case. Then youll need to swap tcases or tcase input shafts to a 7.3 style. And a PCS. Youll also need to fab a little bracket to hold the shifter to the side of the case but that's easy. Driveshafts stay the same. Then if its possible id have someone live tune the engine and the pcs, but if youre halfway knowledgeable the PCS is very user friendly and an afternoon riding around with a buddy making changes and youll have it tuned exactly how you want it.
