" . . . These were sold as an accessory back in the day to quiet valve train noise, prevent condensation rust and keep the top end lubricated. "
That would be a non-GM accessory for 216/235 Chevrolet engines up through 1953 (and later for GMC 6-cyl engines).
They might make the valve noise quieter, and maybe decrease rust (if they do not block the slits in the valve cover), but they would add little to "top end" lubrication.
