Speedometer and gauges

OKay, I took the dash out of the 65 Barracuda to fix the odometer and amp gauge. When I pulled the gauge cluster out, the amp gauge was not even hooked up. Someone spliced them together and bypassed the amp gauge. I put it back to the gauge and when I start the car now the fuel gauge is off ( it showed half a tank before and now shows full tank). Does anyone have any ideas what could be the fault?
The speedometer works but will not turn the odometer, when I took it apart I found one gear that had worn out. Does anyone know where to get speedometer parts for a 65 Barracuda?