Scott : According to the 1960-68 MPC, there was a change on 11/01/67. The RH, which had been C7ZZ-18490-A, became C7ZZ-18490-D, and the LH went from C7ZZ-18491-A to C7ZZ-18491-B.
At the same time, the nozzles with integral A/C, went from C7ZZ-18490-B (both RH and LH), went to C7ZZ-18490-C.
These changes apparently reflect the change from round to slotted holes.
Bob