Found a great article on selecting the right oil for older flat tappet engines. This guy seems to know his stuff. The article is a bit long (29 pdf pages) and can be a bit academic but I found it very informative. The author is rebuilding an old corvair but all of the info is germane to our old Fords. He does a good job dispelling many of the myths I've seen on this site. Enjoy!
I recommend going to the web site HERE and downloading the pdf.
Last month I called Shells lubrication lab enginers and Mobil lubrication enginers lab. This is what they told me that was important enough to remember and share: The best oil for flat tappet engines is 15w 50 unless you live in Alaska or Canada. ZDDP levels are highest in these weights and Shell recomended their Rotella 15w40 and Mobile only recomended Moble One extended performance only in 15w 50. The turbo oil is ok to mix in if you live in Alaska and want to thin it. These oils have basically the same amount of ZDDP as oil made back in the day when your Jeep was built. Is this enough ZDDP to break in a new cam. No! Thats why the factory added ZDDP to break in oil. Once it's broken in then the oils listed above will protect a flat tappet engine. Note the weights of the oil listed again.
This is how ZDDP works: It only works on hot spots in your engine above 500 degrees F. At this temp it bonds with the hot metal hot spots and forms a hardened alloy. ZDDP gets used up very fast and is why engine builders change it a few times while it's still being broken in on a dyno. I'd change your oil at least 3 times durring the first 1000 miles when using a flat tappet cam and also add GM or Ford beak in or assemble lube added as an addative.
The sigle best oil you can buy to run with a flat tappet cam is Moble 1 Extended performance but only in the 15W50 weight. Rotella is good stuff also and even the brand new stuff comming out has been improved way beyond what you would expect. You can't run the thin weight synthetic. You still need the 15w 40. Buy the Mobil 1 and pick up 4 or 6 bottles of GM assembly lube to add 1 to each oil change. If it were me I'd change every 300 miles till 900 then every 1000 miles till you hit 5000. Remember they told me ZDDP gets used up real fast in a moter being broken in. The old cam in my old engine will last only because it spent the first couple of years of it's life running with the same levels of ZDDP of the two oils I told you about and the steel has been turned to a hardened alloy by it. It has nothing to do with the way the cams are made today. It has to do with how they were or were not bathed in the hadening propertys of ZDDP.