I just verified on my 470 engine that the oil gallery is not uncovered. I'm using unbushed lifter bores, Comp 861 (AMC) roller lifters and I have about 0.800 lift at the valve with 1.65 rocker arms.

When you get close to the limit you need to double check everything. We just put the short block together and then spin the oil pump by hand and watch how the oiling works. Make sure you rotate the engine over a few times so you can see how each lifter oils at max lift.