Mopar Muscle Association UK

Didn't this happen before? May be an idea to replace the suspect parts eg
ECU, Coil , ballast resistor, dizzy. One of those or the feed from the ignition, maybe. FBO kit is a pretty cheap set up. Fits as a standard replacement if your car is electronic ignition.
If its points, have they closed up?

Check the UJs either end of the prop shaft. Front one more likely to be shot I believe. That will cause clunking at low speed and vibration at speed

UJ = universal joint. One each end of the propsaft (Long bit, goes from transmission to rear axle )There is a + shaped joint at either end. Try and push the prop up and down/side to side. There should be no movement in the joint. even slightest movemet means thay are on the way out. Cheap service item to replace.