I'm into BBC's now but a while back I played with 350's. I didn't like the idea of my engine inhaling nasty blow-by so I vented both valve covers and sprang an oil leak in the pan gasket. Fixed it three times. On the third strike I went back to a PCV valve and breather combo and no more leaks!

I had in particular one well built 350 +.030, 11:1 pistons, ported and polished double hump heads, double springs with titanium retainers, crane gold roller rockers etc, solid lift cam to the tune of about 400 horses. But it still red lined at 6500 rpm. I would say your engine ain't too mild!

Good luck, Kitz