Bob,
My wife's first car was a 64 -1/2 Mustang coupe. The 64 - 1/2 cars were supposed to have been sold to the public in the late spring of '64. That's before the normal release date of the new model year. Her Mustang had a 260 CI V8 with a 4 speed manual trans. We've been told that the 260 V8 was a 64 - 1/2 only engine with '65s getting only the 289 as the V8 option.
Bruce