Whiteline Com-C top mounts, which are a traditional rubber top hat, but with firmer rubber (like Group N parts), and with the center point relocated to one side. It's not adjustable, but by installing it with the offset center pointing towards the center of the car, we can gain both caster and camber. (See the photo above, showing one of the mounts on the passenger side of our car.)
Having extra camber helps the car to maintain grip in the corners. Having more caster gives you more camber only while the wheels are turned, which (it turns out) is exactly when you need more camber.
On the alignment rack, the car gained almost 1 degree of camber, ending up at -1.2 degrees left and right. Caster also increased by a little over a degree, to 6.8 degrees.
On the street the car feels the same -- I didn't notice any additional harshness from the stiffer hats. The car drives about the same, and I honestly could not feel the additional front grip -- the limits are so high that on the street it's hard to get the front end to wash out at all. A few tail-out donut maneuvers in an empty parking lot showed that the rear is just as frisky as ever.
The big 255 tires fit under the front fenders a little better now, too -- before they were distinctly poking out of the front. Now they're nestled in there nicely.
If you'd like to buy a set of these nifty top mounts, you can (as always) find them over at the Mach V web site.