Well, any dually except the Toyota Buddy axle is gonna need to be shortened significantly.
96 was the last year for the 5.0 in an F-series. If you grab a 97+ you are looking at the Triton engines, not the small blocks, unless you find a 97 "F-250" which was a 150 body, a 250 suspension, and a 351W.
As for carb stuff being "cheaper" or "better", I disagree. I'm building a 5.0 for my mom's Mustang and I had a set of bad FI stuff and no carb stuff. I priced out both systems, and for anything worth having, it was about the same. EFI is easier to set up and more reliable, so unless you already have the carb parts, EFI is probably the better route to go. But then, a lot of guys will say that's an opinion.