Joe,
The weld will very likely show if hot salt blued or maybe carbonia blued (not sure on that one). Rust blue will cover a weld well. I use low carbon steel for welding these things. Make the new tang with some draft angle on the sides to make it easier to inlett. Put the weld/cut in the least visible place. I think it hides best in the radius, but more difficult to match the radius with the new piece. So, the default is to put it right at where the old tang straightens out (the tangent) and then you can make a simple straight new tang.
