I don't know what the emissions laws are like where you are, but in most places that would be a major PITA once a year. If you want big power, it's easier to just save for a supercharger or a set of trick flow heads and aftermarket cams than swapping engines, in my opinion. If you're dead set on a 5.0, I'd just start with a 94-5 since it's got the 5.0 with basically the same interior and go from there. I personally like the 4.6 and don't see it as a bad engine. It just likes different things than a 5.0, that's all.
Tom