I just recently performed this operation on my 59 261 engine. It was also being used with a by-pass filter and I wanted to go to the full flow design. I found a round punch that was close to the same diameter and then went real slow. I started with a small hammer and increased the size of the hammer until the dowel pin moved, then it seemed to a little easier. It went in about 1/2". Hope this helps.
57 Mike
