I use 20w-50 in an unrestored 216.
10w-30 seems thin to me for an engine that old that hasn't been restored. I'd at least bump up to 15w-40.
The 216s are spec'd at 15psi at operating temps. I think the 235s are supposed to run at 30psi at operating temperature.
As HRL said on here once, an engine can run at zero psi as long as the oil being applied to the wear surfaces is replaced to the pump at the same rate.
