With few exceptions very seldom is mixture distribution even cylinder to cylinder,therefore you'll have varying EGTs. Fuel injection and single plane manifolds don't cure this either,I'm certain the 6pack manifolds are pretty far out in this area. First step to avoid killing your headers is add alot of timing,just twist the distributor to 25 initial and determine if your going the right direction. Do you have an infrared gun? Would tell you alot and very quickly let you see the difference.Hope you get it figured out quickly.