Do Super Cobra Jet blocks have higher nickel content than Cobra Jet blocks?

Finding the word "Super" stamped on some Cobra Jet blocks has led some people to believe that the block is a high nodular iron casting or is somehow otherwise stronger than other 428 Cobra Jet blocks. According to several sources all 428 Cobra Jet, 428 Super Cobra Jet, and 428 Police Interceptor engines were assembled on the same production line and this stamping helped identify engines whose bottom ends required Super Cobra Jet components.