Some things to test for , since the new ignition is higher voltage use a clip lead and ground the tip of a long screwdriver and probe the coil, dist., wires, see if you get any arcing.
Look for arc marks in the dist cap and rotor.
A vacuum leak in the advance could cause the advance to be unstable. Could be in the line or dist. Disconnect the line and see if it make a difference.
A leaky intake manifold could cause a problem, retighten the bolts. Same for the carb to manifold gasket. I have sprayed wd40 to check for leaks, see if idle changes.
Check resistance of plug wires, flex them around to check for broken conductors.
This is a large list, but good trouble shooting practices.
