Be sure there is a Ballast Resistor in the circuit from the switched 12 volt source and the positive side of the coil. Without one the points will burn and the coil will overheat.
EDIT: The canister type coil should be mounted vertically so the windings within are covered with the
oil inside which is a coolant. If a coil is marginal or on the verge of complete failure it will often times get an open circuit (fractured or broken secondary winding around the core) that will be problematic when it gets warm from current flow or conducted heat, for instance mounted on the front of a cylinder head. I personally like the "Anti Vibe" coils from MSD that are housed completely in epoxy. With the harsh ride that many of our cars have any edge you can find to fight vibration is advantageous.