Part of the fun of the 7.3 is that there is such a vast amount of knowledge, know-how, & after market parts for them. Anything you want you can freight across from the US. My 7.3 front was sagging & I freighted over a 'levelling kit' - bolted straight on, works a treat.
Having said that, if you find a good 4.2 and like it, go for it - you'll never have to worry about the drive train, but your engine parts/mods will be limited. If you're happy to keep it stock then that isn't a big problem either!