The pertronix only works with the single points dizzy. Ask the part guy for a 68 510 distributor and you can put that thing right in there. I think they are only $120 @kragen/oriely.
You also need at leaste 3 ohms of resistance in your coil + ballast resistors. I have the 3ohm flame thrower coil and it still gets to hot so im adding a .8 ohm resistor.