Let us know how that drilling and tapping idea turns out. I am honestly curious because that dang thing is in there so tight I can't see threads holding up with the slide hammer. Then, how are you going to get both at the same time? (bypass at the same time as full flow)
What Chevy could have done instead is to just thread the hole and use an allen set screw with the proper length to turn it out flush (bypass) or in all the way for (full flow).
As it is, the dowel passage is 1-5/8" long. The dowel itself is 1 inch long. There is really no reason that plan won't work. (except that 1 inch is TIGHT - ask JiM)
