ZDDP - What oil to use in classic cars

On all the classic car blogs is a hue and cry about how important ZDDP is in oil for classic cars. I see conflicting information. So the questions are: Can classic car engines be damages using modern oil? If so, what oils should be used in classic cars and how can you tell.

Some oils, particularly old British Sports cars and motorcycles have a reputation of not tolerating any SM rated oils. Diesel oil like Rotella 15w40 or Delo 15w40 still contains ZDDP and MSO2 and work fine in any older car engines. Penzoil 30HD is rated as an SL oil and not SM so it may work for you if you are OK with straight 30w oil.

ZDDP is an antiwear additive. It is the cheapest good quality additive. There are a lot of others. Modern oils use less ZDDP to avoid potential catalytic converter problems, but they substitute other more expensive antiwear additives.
Modern conventional oils now almost match the performanve of modern synthetics (except in extreme temperatures), and far exceed the performance of even the synthetics of years ago.
Just use your favorite quality SM rated oil (Havoline is my personal favorite, but they are all good). You’ll be doing your classic car engine a big favor.

The urban legend about needing ZDDP for older cars relates to flat tappet camshaft wear, and apparently actually refers to some improperly hardened aftermarket high-performance camshafts.