I was looking in another thread somewhere else that in some posts they were talking about 42 with 45 wheel in it that Forced Inductions made, said it surged badly due to intake wheel being larger than the exhaust. I didn't know if you had figured your problem out or not. if you want the link let me know.
On another note if that turbo doesn't work, theres now a 47 with a T4 flange.