Actually NHRA has allowed many aftermarket parts because of the lack of serviceable stock cores. So much so that many purists are complaining. Aftermarket rockers and solid cams in Stock are a few of the more recent. As far as blocks, NHRA has approved the P5153478AB and Ritter blocks for small blocks and Bulldogs, Kolenos and P5155072AB for big blocks. Aftermarket heads are also accepted for most applications. These people get approval for this stuff, then can't supply it. It's unicorns. Don't blame NHRA.