Oh, you just can't leave us with a broad statement like a "Busa swap" with no pictures.

 

No clue about the speedo, but you got my attention with Busa and rzr in the same sentence! We need pics through this cool project for sure.

 

Internetresting

 

See busa 900xp....old thread but I started working on it again

 

The speed is calculated by the ECU using a proximity sensor on the trans that counts the rotation speed of the diff gear.

 

I seen the pinout for the 900xp and it does indeed go to the ecu, but I noticed on 800 pinout that it appears that it goes directly from speed senor to speedometer...just thinking of ways to have speedometer

 

Something like this might be the easiest solution

Motorcycle ATV/UTV LED Speedometer LCD Digital Odometer Guage Engine Temperature | eBay