There is no "least amount of rewiring" to be had. You have to swap the entire engine management regardless of which way you go.
It simply isn't worth it. Turbo cars are all over the place and you can easily have one shipped.
Saying it will cost less than an '05 STi is silly - when you consider what you are getting for the money spent on the '05 vs. a turbo swapped '96 Legacy done by someone that's never done an engine swap and has no idea what that will entail.... you are getting MUCH more for your dollar buying the STi. A 2.0 will not make STi power and then you have all the rest of the car that totally blows by comparison. Suspension, brakes, steering, interior, etc, etc. To build out a '96 Legacy into a comparable for the '05 STi would be a lot more than just buying the STi. And the engines you are looking at pretty much suck. 2.0's are notorious for rod bearing issues and quite frankly buying a used, turbocharged sports car engine is a huge gamble and therefore a bad investment.
Edited by GeneralDisorder, 13 February 2013 - 12:28 PM.