New motors may take a while for the rings to seal up well Did the block have a torque plate on it when honed? If not it may take longer for the rings to seat On my 511 and 518 C.I. 400 stroker motors I ended up with two PCV and two breathers, one each on both valve covers
Before you start looking at a crankcase vacuum system, verify you don't have a blow-by problem. With both valve covers vented, you should not be blowing the dip stick out of the tube @ 3K, even on a big incher.
Did the block have a torque plate on it when honed? If not it may take longer for the rings to seat 
