If there is oil flow out of the overflow tube then it doesn't sound like anything is wrong. Only a small flow out of the vent holes on each rocker is correct.
Chevrolet never sent much oil towards the valve end of the rockers. At higher RPM's some oil mist does find the valve stems.
In fact 1932 was the first year they put the vent hole on top of each rocker. Before that they only sent oil to the pushrod socket through a felt wick.
