'74 Duster - stalls easily

Orginal engine? That engine has a nylon tipped teeth on the top timing gear, they can start to fall apart at around 100,000 mi. Heat crossover is starting coke up with carbon. Flat lobes on camshaft, heads need hardened seats. This is most probably not your problem, but be aware that all of these things will start to add up. Tearing down my '72 318 right now and besides hemorrhaging oil, have found all of this, and it ran fine.