Had the same issue, pulled the threads out of a marette, drilled a hole through it slightly smaller than the hose ID and shoved it in just before the PVC valve. No more whistle... You may have to experiment with hole size.
It's easier to simply grind a small groove inside the head bolt hole up to the oil hole with a burr, then you don't compromise the integrity of the stud as well. It literally takes 30 seconds to do.
Engine Masters just did a comparison of split pattern and single pattern cams using manifolds and headers on 372 SBC with 10.5 to 1 compression. The split pattern made more power in every configuration.
Some use 340 blocks in the NASCAR Canadian tire series. Ron Beauchamp (team Mopar) told me that they usually pay $500 for a standard bore block with caps.