OK the points and condenser are mounted to a metal advance plate which is screwed to the housing. They have to be grounded to work properly you have a classic symptom of a bad ground the timing is the spark "walking" Pretty easy check take a ohm meter and check if you have a good ground one ohm or less between the distributor and the block itself. Seen the block painted, just a fiber gasket, distributor painted. The hold down clamp is hit or miss, has to be grounded both to the block and the distributor. Main reason newer distributors use a o ring, older say dual points have to have a hard-to-find metal gasket to insure the ground. Only on points electronic distributors do not need a ground at all. Hope it helps