I hope GCG didn't tell you that the install wont need anything changed other than the turbo lines as I'm pretty sure that with the Garret core your turbo will be 17-18 mm shorter. This may not make a difference when working on a C34 but the difference is quite substantial with the M35 if you want it done properly. Talking from a lot of experience there are slight changes as I have mentioned. I also recommend you update you suction pipe.
I do E-Manage(I have base maps to get you to the tuner as well) and injectors(I have a set of Deca 610cc atm for sale at a good price). I use JEZ to do the tune as he is the only one in Sydney that I trust and his done enough of them now.
Talk soon. Don't go for the 30/76!!!....you'll be sorry.
P.S. You will also need to upgrade your fuel pump and hard wire it, Actuator and BOV to get the most out of it.