I received my 1903A3 front sight base from Numrich today.  It looks like it was taken off a rifle by a gorilla with a sledge hammer but I can pretty it up.  Best of all, it slips on with just a little twisting and covers up the dovetail in the barrel completely.

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I will probably fill in the dovetail with JB Weld.  I forgot that the 1903A3 retaining pin engaged a separate key that fit into the top of the barrel.  So to retain the sight base I think I'll drill a retaining pin hole like on the 1903 front sight base.