The first thing that has to be done is get the timing back to where it was. That begins with restoring the advance curve. Hopefully they still have the original springs.
the car will almost feel like it’s missing a couple cylinders then after sitting in gear idling it goes back to normal BUT it comes back. 340 goes in and out of this problem while I’m driving.
It very well could be .
OK. I missed that its a Mallory built distributor before getting my coffee.
Those are more difficult to set up and what I wrote before about Chrysler Built MP distributors does not apply to these.
This is because changing the advance 'stops' also changes the tension on the light spring, and the degrees in before the long looped spring engages. I can walk you through this with photos.