Yep, Ron Butler was his name. He built the Mopar Missile Duster, Butch Leal's Pro Stocker and SS/B 1965 A-990 car and others. Ron was a top notch chassis guy. I forget what the exact technical infraction was with Paul's car. It may have had something to do with weight distribution (too much over the back wheels).
FWIW- Dwight and Al Lee talked about this car. IIRC, it was very light. Lighter than a 6 cyl car with no cage, radio, or heater. The car definitely had more weight on the rear than the front, if there was no ballast. My understanding is that one of the 'tricks' that made it launch was the front spring perches had been moved downward quite a bit. I would suspect this was one of the last factory backed S/S cars to be built to run on super stock springs. The last year it ran, ladders and 4-links were becoming pretty common. I think Butler was trying something new with this car, too, as it was a lot more flexible along the lengthwise axis, than most of his cars teneded to be. I've heard a few racers comment on how the passenger window glass would pop open at the top as the car pitch rotated up on the launch.