Small airplane engines have nitrided steel or hard chrome plated cylinders. I would not be inclined to equate an airplane engine’s break-in requirements to that of the OP’s cast iron cylinder engine. The cylinder bores have the more critical requirements regarding break-in of all engine components. I’d go with the break-in requirements in the original owner’s manual with maybe a light extra push to allow for modern oil protection.
Note too that the latest oils with SL and SM designation do not have enough metallic antiwear compounds (Google ZDDP) to adequately protect the flat face cam followers in the OP’s engine. Modern engines can tolerate these newer oils as they have roller cam followers. The metallic antiwear compounds deteriorate catalytic converters which is at odds with the EPA’s most recent emission control durability requirements. It would be prudent to use a couple of quarts of diesel engine oil with the engine oil. If the OP has resistance to mixing engine oils, then use all diesel oil as the car has no catalytic converter to degrade.