Apparently, there was at least one prototype 1968 Mustang hydraulic 427 with a 4-speed. I believe that topic was discussed on the Cobra Jet forum recently. I recall reading on the SAAC (Shelby) forum (before it crashed last year) that there was also at least one prototype 1968 Shelby GT500 with a hydraulic 427 with a 4-speed. I don’t remember ever reading about a 427 Cougar 4-speed prototype.
The Shelby 427 prototype was built using a production GT500 and was an automatic. It was tested by one of the magazines back in the day. Like all GT500 Shelbys it had a “S” engine code in the VIN. The car is not known to exist, but it could be out there as it was not a Ford prototype. I own the magazine where it was tested and have shared it on various forums over the years.
Well, you might be right that the 1968 prototype 427 Shelby 4-speed was not built because we have no photos of that car that I am aware of, but Shelby documents prove that the 427 GT500 4-speed was planned to be offered for the 1968 model year, for example ^. If you are referring to the 1968 press release cars, I think that 427 car is a different car from the airport TOW vehicle(s).
So, apparently a 427 with a 4-speed was planned at some point for 1968 Mustangs and 1968 Shelby GT500’s, but I have never seen any indication that the 4-speed was planned for Cougars.
Lots of 427 powered Ford and Mercury and Shelby vehicles were engineered and planned for 1968 model year. Then all those plans were cancelled when the strike happened. We are so lucky that the 427 GT-E Cougar was the only vehicle produced. No Shelby Mustangs, Torinos, Cyclones, or Mustangs were ever produced with the 427 at the factory. Piles of paperwork, emblems, warranty programs, advertisements, etc were produced for all those vehicles that never existed.
