What's the purpose for the big turbo?
Do you want a big turbo so you can tell people you loose races to that you have a big turbo?
On the street, at street boost levels, a bigger turbo will be slower than a smaller turbo.
A big turbo needs a 9.5" converter and big injectors and at minimum a large wastegate puck in the elbow. Heads, a good intercooler a and 3" downpipe are good to.
Big turbos are great for turning up the boost to 24 psi. Piddling around on the street with a stock motor and 12" converter at 16 - 18 psi, you're better off with a stock or TA49/TE44 turbo