You will definetly need more fuelling!

dont bother with narrow band guages what you need to do is go to a rolling road (dyno in us?) and get them to stick a wideband on the exhuast and go for a run!

After my turbo conversion I found out I was running too lean! and I opted for a extra injector which was connected to a Scooby MAP sensor instead of a boost switch. The benefits of the MAP sensor is that it can see varied amounts of boost so it will send a signal to the MF2 (or any other programable injector controller) so you get extra fuel only when you need it! not all the time u see boost!

some pics: