gunboat57:  Why don't you take a piece of mild steel, like a spike, and hammer some flats and file to shape to make a "key" or spline to fit the groove of your 1903-A3 banded sight.  You could have this fit your barrel dove-tail and angle its base to correct for the dove-tail not being at "12 O'clock".  Once the spline is fitted, the barrel band could be tapped into place.  A filed notch on the spline would allow the band to be locked into place with a cross-pin.