In my 1987 M103 I use 15-40 dual rated for gas or diesel. For me the secret is in the ratings. I want CI-4 /SL or SL/CI-4. I do not want CJ-4/SM. You will find oil recipes change but they call the oil the same name as with the old recipe.
Every one has an opinion on oil and this is just mine after many hours spent reading . The latest oils are excellent oils for roller cam engines. Not sure if this is true for cam in my engine. I use a Mann filter.