blken8k,
I'm not saying you should take chances with your classic "Flat tappet" car. Of course if you never run the engine, you would eliminate all chance of damaging your precious flat tappets, or you can throw caution to the wind and just enjoy the car without being so anal about something that is probably pretty irrelevant considering the mileage you are putting on the vehicle on an annual basis. Remember, everytime you start the engine you are risking that some part will break. If you drive the car and enjoy it, then there is always the risk that something will break or wear prematurely.
I would think that someone has already bottling a zinc additive that you could add to any modern synthetic oil that would give you the best of both worlds...the zinc to protect you flat tappets, and the extended, superior lubrication properties, and heat tolerance of a modern synthetic oil.
...Richard