For a short time, the points will be OK, you don't want to run them on 12 volts all the time. The coil would be the biggest concern. I think a 6 volt one might go bad really fast. The points are stepped down to 8 or 9 volts by way of a resistor wire on the truck. For testing go for full voltage.
Check the valve adjustment for rough idle and/or carb adjustment.
The starter will live just fine on 12 volts as long as you don't stand on it for extended periods of time. Normal use is OK.
Voltage will not hurt idle, it should make it better with a hotter spark.
joe
