I believe there are actually two different types of
oil pumps (3 if you count the stock version): HV and HP (there may be a HVandHP pump as well). The high pressure pump may cause
oil to build up in the valve covers, if you just go with a high volume pump, AND locate the pickup correctly (it may need to be extended for certain pans in order to prevent early cavitatation).
Using a HV pump with an extended pickup and edelbrock heads, I have no problems, without restrictors.