Yes indeed. It is a Driver's side only, spark plug wire extention/relocation bracket for a 66, thermactor equipped car, SJ built, CA dealer-delivered (LA in our case), regardless of GT or Standard option. May be exclusive to A Codes, not positive on this part, but I do believe I've seen it on C Codes with thermactor emissions. Could have been added though, as smog was required every other year in CA for quite awhile.
Function:
It screws onto existing valve cover tab (earlier low profile/rounded variety) and relocates the bank of 4 wires away from the smog air logs. The later valve covers were tall enough (squared off a bit more too) and no longer needed this for the wires to stay off the log tubes.
As I previously stated also, going to give Bob Mannel credit for the definitive info and great pictures in his book (Chapter 6).
Hope this helps get that pesky question out of your thoughts for awhile now. Know those well...!
-Lance
