So my 85 xt 350 has a KPH speedo. I'd like to change it to a MPH speedo. Is there gearing inside the motor case that will need to be changed as well or is it as simple as swaping it out with a MPH unit? It appears that many other Yamaha speedometers are very similar off of other bikes (250, 600, 550, tt, ect.) I am assuming they are all pretty interchangeable?