If you changed knuckles without modifying the rack/tie-rod assembly, then you almost certainly have different bumpsteer now than stock. I can't say what it is though without exact parts measurements or measuring the steer itself.
It's all easy to visualize once you've moved things around in a 3D suspension model, but I'll try a little explanation. The tie-rod axis must intersect with the instant center of the control arms (or strut) to have zero bumpsteer (illustrated in pic). If you look at the movement of the assembly as it goes through bump/droop, it becomes clear that the length of the tie-rod as well as its initial angle determines dynamic angle, and consequent steer effect. To modify the initial tie-rod angle, you need some kind of bumpsteer kit which will let you adjust the height of the outer tie-rod pivot. Alternately, you can change the height of the rack (usually more difficult). To modify the length of the tie-rod, you obviously need to either change the width of the rack, or the steering arm on the knuckle (neither is usually practical). There are pics that illustrate all this movement in my RCVD text, but I don't have a scanner here.
Bumpsteer is fairly easily measured, although it takes some time to get the car set up to take the data. Basically you put the car on stands, pull the springs & swaybar endlinks out, attach a bumpsteer gauge to the hub, and just measure the amount of steer you get with dial indicators as you run the suspension through its range of bump/droop. If you have a means of adjusting like a bumpsteer kit, then you change spacers & test again. Change spacers & test again. Etc.
http://www.maximummotorsports.com/st...roducts_id=193
The simplest thing to do is just adjust the spacer stack to minimize any steer, although you can tune it for some desired handling response if you want. OEMs use roll & bushing compliance steer effects to tune understeer into their vehicles. If you're getting dynamic toe-in during roll at the front of your SVX, it could account for some of the 'plow' you're feeling. I'd advise measuring/adjusting the bumpsteer for this reason alone, cause you can definitely feel these effects on track.
Now, that being said - I doubt bumpsteer is responsible for power-on steering shudder. I'd look at all of your suspension bushings, steering rack mounts, and the ages-old strut dampers as a cause first. Usually when there is any kind of shudder it's something to do with the combination of all the rubber and damping (or lack thereof) in the system, from the tires up.
Also.. 70/30? Really?
