Hi D100, and welcome to the forum. Take a look at this recent link, apart from showing that we are active participants in discussions, and don't necessary agree on things all the time, there is also some references to ZDDP. The problem related to catalytic converters is the newer demand that the life expectancy of a cat should be a minimum number of miles (don't remember the figure), and there are many additives that will kill the cat over time, zink, phosphorus and sulphur among others. Lead is the biggest killer, that is why we use unleaded fuel today. As our guru Dan says, the API standard states that there is a backward compability for motor oils, and the question is if all the horror stories about low levels of ZDDP are correct. ZDDP will eventually kill your cat over time, but I don't exactly have the impression that the shortened life of a catalyzer because of ZDDP has been a great theme for discussions! I have been in contact with Red Line oil about the contents of ZDDP in their oils, as I don't have a cat in my car! (I have been getting the impression that Red Line is a very expencive oil in USA compared to many others, over here they're ALL priced beyond hilarious!) Anyway, they recommend 10W30 for the slantsix, and they have formulated their synthetic motor oils with sufficient amounts of ZDDP (~1200 ppm). If you live in a climate zone with cold winters, do as many on the forum does, use a good synthetic oil, Mobil1 0W30 or 5W30 seems to be a favorite, or stick to the 10W40 you use now. The synthetic oils have a built-in multigrade effect, remember that the lower, first number describes how the oil behaves when cold, the second how it behaves when hot, so don't be afraid to use an oil starting with 0 or 5, it will just flow better when cold! The matter of oil viscosity and synthetic or not has been a subject in many posts in the forum. I think there is a general concensus that a good synthetic coupled with the correct type of oil filter with an internal standpipe (important!) will make your slantsix happy for years to come. If you use a ZDDP additive, you will have to balance the amount you use against the lifetime of your cat. With no concern for a cat in my car, I'll personally stick to the ZDDP for a while yet, until experience with the new additives can be evaluated over some time and tell me otherwise.
We have an article section that you should read through, and in each section in the forum there is a FAQ (frequently asked questions), where you'll find many links to important subjects. We have a very nice search function that will let you find answers to most of your questions, there are more than 100.000 posts in the engine section alone! Don't hesitate to ask, there is no such thing as a stupid question, but there is of course a lot of stupid answers outside this forum!
Olaf.