The unusual features are the white knobs, the same as the mono preamp, and the location of the Dynakit script logo in the brown strip along the bottom of the faceplate, just to the right of center, as opposed to being in the brass area below the selector and volume controls. Everything else about the preamp appears to be typical PAS.
The history buff in me is fascinated by this, as I have never seen one in the nearly 40 years I have been fooling with Dynaco amps. Does anyone know more about this unit? I am wondering if any of these made it into production as pictured in this ad or if perhaps the knobs and logo were changed before the first ones shipped, as 1959 would be the year that the PAS was introduced. Trivia maybe, but hopefully I am not the only one to find it interesting.