I'm not adding a plate to the bottom of what already is an AS plate base. So, I machined the part to extend the existing dovetail geometry the full length of the part. I used a 1/2" diameter 45 degree dovetail cutter and carefully blended it perfectly to the original surfaces using my Bridgeport Milling Machine. The newly exposed area is raw aluminum but that's OK with me. A little Sharpie will do the trick. Now I can clamp anywhere along the length of the base including right at the balance point that was previously out of range.
