With a draft tube which only works well at highway speeds and only if it isn't clogged with crud, 3,000 mile oil changes should be seriously adhered to. Crankcase contaminants will degrade the oil at a much higher rate that an engine which has a proper PCV system.
Even engines built later than the mid-fifties with full flow oil filter systems and PCV systems need to be changed every 3,000 miles.
Modern engines of today do not require 3,000 mile oil changes. It has nothing to do with what kind oil is put in them.
It has everything to do with the advent of computer controlled electronic ignition, fuel injection and timing.
Carburetors, and points points wear out significantly over a short amount of time and cause increase of oil contaminants in the crankcase.
I have driven 6 modern work trucks over the years for up to 187,000 miles without ever needing new spark plugs. They likely didn't need new plugs when they were sold at auction (many of them did need new transmissions however). Try that with a Stovebolt or any other vehicle which has a carburetor and points without Triple A.
