Zinc has been pulled out of rotella every year for the last few years, so the discussion regarding rotella here is irrelevant.
There are two ways to meet the ZDDP lub requirements of the flat tappet 4.0
You can use hi zinc content oils or zinc additives. there are specific amsoil race oils, also there are a small few generics that have zinc as well. I've been told petro cans brand as it, but I've never used it myself.
The other method is to use an oil that is spec'd for a flat tappet engine. North american standards stopped specing their oils for flat tappet engines several years ago. No matter what an oil bottle says for american standards, you have no way of knowing if it meets flat tappet lubrication properties.
Europeans still test for flat tappet properties. You can tell if an oil is european tested by the letters "ACEA".
Flat tappet specific ACEA standards are A3, and B1. So, if you can find an oil that has ACEA A3 or B1, you have an oil that has been tested and meets flat tappet lub requirements.
A lot of synthetics have the ACEA ratings. Just be carefull which ones you are looking at.
Lastly, be carefull when using zinc additives. Zinc is detrimental to cat converter life. To much can significantly reduce the life of your cats.
The 4 litre was the last flat tappet engine left in production in north america. Most oil makers simply dont test and lable most of their oils for flat tappet testing. Unless they are testing them to euro standards of course.
Dodge has had an influx early cam failures during the last 5 years of the 4.0, and it has been attributed to todays oil properties.
Corey Kruchowski a known 4.0 builder on here had 6 out of 20 cams failure about 2 years ago. He changed oils for his customers and has not had one come back since.
The ZDDP issue has been known, and been around for years with the muscle car crowd.
The issue that is unique to the 4.0 is that we have flat tappets and the catalytic converters. Making the use of large quantities of Zinc somewhat risky.
There is a lot of info on this stuff all over the net. A morning with google will educate anyone interested in this topic.