alot of times we drill the lifter front galley plugs to ge air out small hole .035 or so and GM did this to .i do it to throw more oil on the the chain set. it help put oil on the thrust were the top gear rides on the block or the thrust washer to the block and some guy s re use the old plugs you want to make sure they do not get mix up i have never done this but have seen it done. when your eyes get old they are hard to see i all ways checks this if i reuse the old plugs