Back in the day (50 years) iirr engines came with non-detergent oil, after 500 miles it was changed to detergent, 30 or 40 weight. Nothing like out there today.
bu the question is did that none detergent oil have ZDDP in it? My guess is yes as flat tappet camshaft failure was one of the reasons it was added to the oil somewhere in the 30's according to current information. Previously read info claimed 1920 or so.
Also 50 years ago was 1972
and I believe the era you were referring to is the 1940- to early 50's
