I don't recall any multi-weights until the mid 70's. You can still get non-detergent oil.
In 1953, Amalie was the first oil company to introduce a multi-grade motor oil: Imperial 10W30.
so there really is t any harm to collect old oil cans at yard sales and use the oil for breaking in flat tappet cams. heck you fire it up, run it for a bit and dump it anyway. jim