Fouling Plugs

Gidday, I'm having a bit of a problem with the 383 fouling all its plugs. It is currently running a factory electronic ignition with an orange box, I have put new leads on it & coil (just a cheap one but), the carb is a 750 vac Holley with size 70 jets & is running a 4 post ballist resistor.
Being that I'm fairly new to this style ignition, is it normal for the plugs to foul fairly easy? I'm thinking of putting a full MSD setup in it if I can't work it out or if this is normal. I haven't had the dizzy out to make sure it is working properly but the rotor & cap are both in good condition.:banghead:

Your comments please!

What are they fouling with?
Oil?
Grey deposits?

Can you post a picture of one?

Cheap gas causes grey deposit buildup.