Well you asked a question that you think you have the answer to, or are not sure if it is true? If you trust this post on Wikki, have one drilled out and report back to us, or ask a smith. Try the gunsmithing forum. I would be interested to hear from one of the qualified smiths on that forum.You still have to decide which 20 gauge 870 barrel will fit the old 58. As far as the stock goes? I don't know. I would cut the stock to fit the youth and keep the removed portion til he/she grows.