Did you pre-oil the pump, or maybe pack it with Vaseline before installing it? If so, you should have no problems pressurizing the system with a drill motor. It sounds like the oil distributor was doing its job- - - -protecting the lower end while restricting the flow to the top end, at least somewhat. Most likely, there was probably a little oil getting to the head with the engine at highway speed, just little or none at idle. If you have tightened up the main and cam bearing clearances (Cam bearings are VERY important) the oil flow to the top end should improve.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!