[bigblockv6]

Valve rotators were used to keep valve seats clean, they're mounted on the bottom of each valve spring. Used in bigger truck applications, though in later years an HD305E was offered with this feature. 4 ring pistons were used on all 305C engines from 1960-74, again this was a big truck feature that had one extra compression ring, it also phased out the 3 ring pistons in 305E engines for replacement for the purpose of standardization around 1970-71. Pete Chronis Northern Cal.