The original 6V ignition with points and condenser will have a coil that can produce maybe a maximum 30,000 (30KV) volts but it only takes around 8-12KV to fire a stock spark plug under normal load.
If you want to buy a higher voltage coil, the manufacturer recommends to replace the stock points with their PerTronix Ignitors. You have to select the correct coil and ignitor for you engine and battery voltage (6 or 12 volts). If you want to use your stock points then you have to select the coil with the correct internal resistance. Even if you find a higher KV coil that doesn't burn up your points you also have to make sure your spark plug wires can take the extra KV. A plug wire can induce voltage into a nearby plug wire causing cross-firing...truck runs bad.
Here is a clipping from an article I read:
Choosing The Correct Ignition Coil.
For specific recommendations we contacted our pal, Don Lindfors, at PerTronix to get the straight story on coils. As he explains, PerTronix offers three oil-filled, canister-style coils and they are identified by the ignition system they are suited for:
The Flame Thrower 40,000V coils have internal resistance rated at 1.5 or 3.0 ohms. The 3.0-ohm coil should be used on PerTronix Ignitors installed on four- and six-cylinder engines while 1.5-ohm coils should be used for eight-cylinder applications. These coils can be used on virtually any inductive (non-capacitive discharge) ignition system.
Flame Thrower II coils have lower resistance, 0.6 ohms for use with Ignitor II ignition systems as well as many other high-energy ignitions. The low resistance helps to produce up to 45,000 V. This higher voltage allows larger spark plug gaps for added power and better fuel economy.
Flame-Thrower III coils were developed for use with the new Ignitor III electronics. The extremely low resistance of 0.32 ohms results in 45,000 V and a coil that charges to peak, current typically 30-70 percent faster the other coils. It should be noted that these coils are compatible with Ignitor III electronics only.
