My '37 has a 1970 250 ci engine, I've been running 10w30 synthetic oil for 26 years now, no extra additives. The valve spring pressure is weak enough it doesn't need anything else.
The zinc additives for camshaft wear was raised when the the muscle cars started getting bigger camshafts sometime in the '60s, in the late '90s it was taken back out due to catalytic converters and emissions. The levels now in most over the counter oils is back where it was before the muscle car addition.
A stock factory built 216 has 16-20 lbs of valve spring pressure with the valve closed, and 38 to 44 lbs with the valve open. The extreme cams that need the added zinc additives has upwards of 300 lb springs with valves open.
