Where i drew the arrow, there is a 1.375" hole that used to have an old drain pipe connected to it, (it is now clearly capped off, and very common on old blocks). And you have valve covers with no holes for a breather or a PCV, but you do have a breather on the front of the intake.
So it looks to me like you need to either put the old drain pipe back on, or get some valve covers with holes for a breather and PCV