If you have the OLD ECU you can simply fit a new set of generic instruments and set them up for the current mechanics.
Spurred on by threads from folk who suddenly find themselves without a working Speedo or Tacho. And given more of a kick following some emails from a guy here in Spain @drctjcp - I have decided to have a bit of a play adapting a UNIVERSAL speedo to the R3. So I went onto ebay and found a CHEAP...
www.r3owners.net
If it is a Post 2010 CANBUS ECU then you have to retain the OEM speedo as without it the bike will not start.
If it were me. I would give thought to the complete instrument change. Whilst I appreciate the original aesthetics may be pretty nifty - the irritation of the ODO being off would annoy me.
How much overall difference in ratios - including the wheel diameter change?