I would have to say that installing the is300 gauges would be very difficult to say the least, if possible at all.
The g20 does not use any muliplex modules in the gauge cluster to function, it receives very simple seperate signals for each light/function. I am assuming though that the IS300 uses an integrated multiplex control module inside the gauge, which would mean that the signals it receives are complex pulse signals(similar to your computer router), and are decoded inside the gauge. If this is the case, it would be impossible to get most if not any of the gauges to function at all.
I'll take a pic of my gauge in my car later today. I'm pretty sure it will be very similar to what you're looking for. It's much sportier and sleek than the factory p11 gauge, and the best part is that everything works, fits perfectly, and looks totally factory!