73 valiant runs good then randomly dies

Your distributor, if it is original, will have a tag on the side with the part number on it. You can keep your present distributor (though it may contain the problem part) or pick up a brand-new Chrysler unit as described in the linked HEI upgrade article.

One way of diagnosing problems like yours is to use a hair dryer or incandescent shop light to heat up the ignition module (good and hot!) before trying to start the car from cold. If the bad behaviour now happens even when cold, you found the problem. If not, try it again on the ignition coil. If not, try it again on the pickup coil in the distributor (remove cap and rotor to get clear access to preheat the component).