Clamp one scale to the tang, then drill through the tang into the wooden scale. Then clamp both scales to the tang, and drill through the scale you already drilled, through the tang, and into the 2nd scale. After you try a dry fitting of scales and pins, epoxy everything up, line up and clamp scales to the tang, put in pins, peen lightly, and let it dry.
Once it's good and dry, you can sand down the pins and shape the handle how you want it.