Strutter,
you mentioned that your disc tends to walk around on you, and I have the same problem. My disc is similar to Ballistictips' s disc,but the angle of my disc axles(not a farmer, probably not correct terminology) are much more severe. They are adjustable on mine but I was told that I would break up the ground better/faster if I kept them pointed in all the way. So Ballistictip, if your disc is working good, then I can probably set my blades more like yours and cut out some of the disc' s " walking" .