My point of contention was moreso your declaration that a drilled out frame would be safe for no-fat GC rider, but not for a Clyde. Without knowing the design and condition of the generic vintage frame that is to be used, the metallurgical and mechanical engineering aptitude of the one choosing what size holes in which quantity are going where, and the equipment being used to make said holes, I really have a hard time understanding how one can put that safety limit where you put it.

My thoughts don't have to be twisted, they can be directly applied. A lighter rider's weight is indeed less likely to break a frame, but the safety margin from the manufacturer is there such that a rider at or slightly over the limit is not at risk of a failure. That doesn't mean that ad hoc metal removal should be broadcasted as safe, or that without without far more thought and calculations present in this thread we can give it a safe limit, simply because there is more of it than was needed.