the diesel still has about 1200 ppm but down from about 1400. so its still ok to use in engine with light spring psi, but i would add something if you have a double spring or use a race oil.
Most all diesel oils have an API rating for auto use too. If you buy a diesel oil with an SM rating then it only has a max of 800 ppm, the current multi-weight Rotella T is SM rated.
The only sure way to ensure a certain level of ZDDP in your oil in excess of the API service rating limits is to get a specialty oil that DOES NOT have an API serive rating and advertises ZDDP levels. Regardless of what the marketing label on the front of the bottle states it's the API serive rating that is going to determine the ZDDP level. The EPA monitors this and the fines to the oil companies are significant if they are violated, the marketing folks that design marketing labels on the front of the bottle and make claims aren't held to the same accountability.