I agree that older engines (with filters) can use these newer diesel formulations.
But my 216 has no filter - so I don't want to pump suspended dirt through the mains and rods. I want it to fall into the pan where regular oil changes will prevent sludge build up.
A wise old man once told me "the best oil you can use in your hobby car is 'clean' oil." If you are going to change often one doesn't need to pay for 'long/extended life' formulations. Traveller SAE 20 and SAE 30 can be had for $2.5 a quart (in the two gallon jug).
They also carry a CJ-4 grade for 3 bucks a quart:
TractorSupplyCorp When my car was running in stock trim I would fill it with SAE 20 in the late fall before the snow season. This would allow me to drive on nice dry days (in the winter) and the car would be ready to go in the spring. When summer approached (and temperatures rose) I would drain and switch to SAE 30. I suspect my service interval was between 500 and 700 miles.
Based on my research API SB (for pre-1951 engines) is nothing but mineral oil and ZDDP. An obsolete oil for an obsolete engine.
