I haven't seen anyone do this swap, but it should be feasable. It'll take a little wiring work as well as the associated parts to make it work.
The 2G bikes get their speedo signal off the countershaft sprocket. There's a sensor on the countershaft end and a pickup in the countershaft sprocket cover.
If you look at the picture below, you can see the sensor and wiring just above the second knuckle and to the right of the crimp in the clutch hose end fitting.