There is more to the champ cars sway control than just a single pivot point. If you look closely you'll see that the part that the bars attach to will also move back and forth, not just rotate side to side. The Revo assembly is similar (as you pointed out), and it too allows back-and-forth motion.
Ok, I had a big long explanation going on, and I just deleted it all. Let me try to distill it for you...lol...though it still ended up being kinda long...
Your ultimate goal is to lessen body roll and keep all the tires as planted as possible as much as possible.
You get rid of body roll with either really stiff springs, a sway bar, or by moving your shocks/springs as far out as possible, both top and bottom. Or a combination of those three. If you completely eliminate body roll you will have a very rough handling rig.
Springs ~ Really soft (think old Cadillac) makes for a smooth ride but allows body roll, transfer of weight (not always a bad thing), and changes several other things that can screw you up. The plus side is that it handles bumps and dips well. Really hard (think race car) makes for a level, predictable ride on smooth surfaces. The down side is that bumps and dips can easily upset the car, bouncing it off the road.
Sway Bar ~ Essentially a springy link between the chassis and suspension. Force from one wheel is transfered to the other in an attempt to keep the vehicle level. Too soft and the body rolls, shifting COG and suspension geometry. Too hard and every little thing that happens to one wheel will happen to the other. Thats bad.
Shock/Spring placement ~ If you've ever goofed with the shocks on your rc, you know that moving them inboard will soften the springs and lenthen your travel. Moving them outboard will stiffen the springs and shorten your travel. To combat roll effectively, they need to be as far out and as straight up/down as possible. This puts the spring force further away from the roll center and lessens their effectiveness as a pivot point for the chassis to roll on.
Take a close look at the real life cars you are trying to emulate with your scale reproduction. Rally cars have body roll when they are off road. They have to because of the rough terrain they run on. They need to keep independent suspension travel to keep the wheels down and maintain traction. Indy cars and Champ cars run on smooth asphalt or concrete. They don't need lots of suspension. And, because of thier speed they have downforce to help keep them planted. In fact, they are so stiff that picking up one wheel only a few inches off of the ground will cause another to lose contact when the car is not moving. I've seen this first hand, and nearly crapped my pants when it was pointed out to me.
