That's about the time frame that the Marines in Yuma were getting them -- the "S" model -- they were SO HAPPY to finally have an F4 they could dogfight with ... can't remember the technical details -- something to do w/ the wing (?), but that's what they said.
The "S" had slatted wings (the so-called "soft wing"). They took 265 "J"s and upgraded the AWG-10 radar to sorta-digital (AN/AWG-10B), scabbed on formation lights, put a strap under the wing to effectively "zero-time" the wing, put new outer wing panels (with moveable slats), re-did the inner wing panels with moveable slats, put in smoke-less J79 engines (J79-GE-10B) in and some other stuff. The aircraft would turn very well without buffet (the AOA gauge was also replaced with one that went up to 30 or so units). The downside was that the slats added a ton of drag, and once you lost your energy, it took a long time to get it back.
One thing the smoke-less mod did to the engines was to make them more prone to compressor stalls at high AOA, plus the products of combustion were changed and the gasses coming out of the exhaust caused your eyes to hurt and water when you walked behind the aircraft when it was turning (or when the wind was blowing the wrong way).
