You're looking at a full teardown if you can't get airflow through the rear cam bearing. No shortcuts are possible. There is a large-diameter oil gallery that's drilled through the lifter bores front to rear on blocks set up for hydraulic lifters, and something is blocking that passageway, most likely. Another option that would not require removing the engine would be to swap to a solid lifter cam and the appropriate lifters, but I'd still be spooked by the lack of proper oil flow. Since this is a brand new engine, just bite the bullet and do a complete disassembly to correct the machine shop mistakes.
Jerry
