I just read that the nail heads had very restrictive exhaust ports so as long as it was a blown engine this was thought to help. I couldn't find any info telling if it worked any better but I doubt if it did.
Pinto Power! 😀 I have one sitting in my shop with a custom aluminum valve cover, Offy dual port intake topped with a 390 Holley 4 barrel, Racer Walsh cam, and headers.