Chris : If the Hertz uses a 1" spacer, like the other 1966 A and K codes, the correct studs are as follows :
Part # 88471-S ; overall length = 2-1/2" ; 1/2" of 5/16-18 thread ; 5/8" of 5/16-24 thread. Picture attached.
None of the Reproductions I have seen are technically correct, as the lengths of thread are incorrect. However, once installed, who will know.
Hope this helps.