3 years ago, I took a brand new 660 Special Edition and built a turbo kit, and coverted to EFI using a Megasquirt ECU. The goal was to sell a bolt on kit that was reliable, and made great power.
In the end, I pulled it all off and returned the Rhino to stock. I still have everything sitting on a shelf collecting dust.
In my opinion, the turbo itself is the biggest challenge. I am sure it can be done, but there were no turbos readily available that met the needs of the Rhino. If you get the exhaust housing large enough, the compressor side is too big. If you size it for the compressor, the turbine is too small. It actually needs to be built like a diesel turbo, large exhaust with a small intake, relatively speaking.
Here's a pic on the dyno tuning the EFI.
By the way, exact same turbo in C&G's Teryx kit. I have two of them, anyone want to buy a cheap turbo?