No reason to get one's panties bunched up over a Chevy question, IMO.
Physics applies, regardless.
Can't really be too informative on that lifter valley can, but the Gen1 SBCs were prone to be leakers, especially intake areas & valve covers.
Some of that seems to me would be crankcase pressure.
That lasted into the '70s - there's one from '79 (with a Targetmaster crate motor) in my K10 plow truck.
But decades ago on my '73 Z28, after going through it and getting serious about leaks, its motor was dry up top and didn't have that separator.
It would weep slightly at the rear main seal; the K10 weeps at every seam.
Stock PCV, no pan evac on either example.