The panhard bar prevents the rear end froms sliding side to side. Even with the stiff leaf springs, they still twist torsionally allowing the read axle to literally move side to side.
THe Panhard bar is adjustable and keeps the rear end Exactly where it needs to be.
Also, Kenny Brown just released (or soon to release) a X-Brace for the competition (L). It will significantly stiffen the chassis. Many people say that the (L) has a full frame and is Stiff, well that's kinda true, but it still FLEXES ALOT under HARD Cornering.
The stiffer the chassis is, the better the vehicle will perform and handle. a Stiff chassis will allow the suspension to do exactly what it is designed to do, and not allow chassis flex to make the suspension feel mushy.
X-Brace:
An example of chassis Flex. The Ground effects are supposed to line up. Here you can see how much the chassis is flexing.
NOW, why on earth an I putting this stuff on a SRT-10 page. Because our trucks really aren't that much different. Both will benefit from a stiffer chassis. Both have leaf spring rear suspension. (regardless of the placement of the shocks) the rear end will move side to side.
Lastly, recently someone noticed that a stiffer chassis reduces 60' times. They installed a 6-point rollbar (not cage) that dramatically stiffened the chassis, He dropped his 60' times by almost a tenth. While that may not seem like much, it is well documented in the "lightning world" that a one tenth drop in the first 60' will result in a drop of two tenths off the 1/4 mile.
.10 drop in the first 60' = .20 drop at the end of the track.
http://www.f150online.com/forums/showthread.php?s=&threadid=188933
THere is some information to think about.
