I've just worked on two 67's, Nov and Feb builds, neither had this plate. As stated this was a 68 thing, possibly late 67. Take a look at your donor car wiring - if you have the inline fuse, that will pull power from the ignition switch as Marty stated and you don't need the z plate with breaker. How "correct" do you want to go? Obviously a period factory Ford system is better than after market or a Ford over the counter/dealer installed add on. You can certainly stop there. Next would be related to revisions over time to wiring (as this thread discusses). Another is related to pulleys, idler, and brackets, particularly with the 289 - there were a lot of changes (see Mannel's book). What plant, engine, and build date?
Some pics might help. From a Dearborn Dec 66 AC car:
First is the fuse box with no Z plate/circuit breaker
Second is the inline fuse tapped off the ignition switch
Third is a "plate" for mounting a relay that is screwed to the windshield washer motor bracket. A little hard to see this one.