Whether you use a spacer . . or not. Spend plenty of time making sure that the right and left scales have equal lengths and are virtual mirrors of each other. At that point, you can pin and bond them into place. After patiently waiting for the bonding agent to dry, resort to hand sanding. Wrap the blade in painting tape, clamp the blade in a vise, and then use strips of sandpaper to round the top, bottom, and sides of the handle. Blend all sides evenly. Step away from the work for an evening or two, think about your next step, and the proceed cautiously and slowly.
In the end, you will have a very impressive knife. Jut take your time an finish it slowly and properly.
Mike L.
LoGiudicecustomknives.com