Let me try to clear this up. Herb Adams is talking about a race car where rubber bushings are taboo because any compliance in the suspension cannot be easily controlled or have predictable behavior. Consequently, hard or solid bushings are used in the shackles, and as Herb points out, he recommends a spherical bearing on the forward eye to allow rotation. With that scenario, it is his opinion that a lateral locating device wouldn't usually be necessary. So far so good...
With a street car, those hard bushings and spherical bearings would transfer too much noise and vibration, not to mention that maintenance on those type of joints would not be practical. That is why OEM's use rubber. They want comfort first and performance second.
With rubber bushings comes compliance, and that can be okay until your clearances get tight (tire to fender for example) or you put on tires with more grip. You do all recall I'm sure how crappy tires were back in the late 1960's? With more grip comes larger forces and then you come up upon the weakest (most compliant) part of the suspension, the rubber bushings.
As we have covered very thoroughly I think, some rubber bushings are necessary, and some bushings can be upgraded for more precise control of the suspension. One can assume that most of the lateral movement in a leaf spring suspension comes from the rubber bushings in the shackles. It would also stand to reason that the longer the shackles, the more lateral movement. If you just had to install those trick polyurethane bushings, put them in the shackles and not in the front spring eye.
All I am saying is that if you want noise and vibration isolation AND more precise axle lateral locating, you can use a Panhard bar... The Panhard bar can also help to lower the roll center of the rear axle, but that is a whole other story...
Hope this helps make it more clear.