With apologies, it is hard to rely upon the prior owner's mechanic's alleged automotive knowledge and detective work. To the extent possible, it might be helpful for you to confirm your vehicle's state of tune/mechanical condition and whether there have been any modifications, e.g., pertronix. Pictures might fill in some parts of the puzzle.
Although my first suspect would be the coil and coil connections (including ballast resistor) a bad or loose condenser could also cause an intermittent stalling condition. If it has not already been performed, consider inspecting the condition of ignition points, rotor, distributor cap, ignition leads, spark plugs and coil connections - all of which is de rigueur in most shop manuals as part of a routine “tuneup.” If you are satisfied that everything is fresh and properly adjusted, consider swapping the coil with a known functioning unit. This. of course, does not guarantee a fix, since it is not impossible for fifty-year-old wiring to loosen or shed some insulation at or near a ground. The same holds true for a coil that might have seen decades of service and exposure to the elements.
…and distributors are wearable parts, it may be 50 years old & not keeping proper timing or advancing evenly.
I had the same cutout problem for months before it was resolved. Please refer to my previous posts.