pre-oil problem

[Heveyb]

I'm scratching my head here. I've got a brand new crate 350 that I'm putting together and am trying to pre-oil it. Problem is that after a few minutes of spinning the oil pump with a drill and pre-oil adapter I've oil got oil only to the valve train on the 2-4-6-8 side of the block. Those rockers are dripping, the other side is totally dry at the rockers. Is there an oil passage in the block that is obstructed?? There is oil around the lifters on both sides but nothing making it up the push rods. Anybody seen this before? Appreciate any insight...