I run Milodon billet oil pumps. In my experience you can't fit these with the same torque settings as the iron ones (bolts to block), they will bind. If my memory serves me correctly, we torque ours to some thing ridiculous like 15 inch/pounds (yep INCH/pounds). Needless to say we always use some sort of studlock on the bolt threads. I don't know what the manufacturers recommended torque settings are, I tried to find them online but haven't been able to. Previous to all this, a buddy of mine had the same issue, he had problems priming the oil on a rebuilt motor and warned us about this.
I've also tried gently snugging the pump up when the motor was on the stand and winding the pump with a priming shaft by hand. It doesn't take a lot of torque to put these pumps into bind. I have them on two engines, fitted with a gasket to block and it's the same with both pumps. I have had no issues otherwise, they work fine.