I think U, D, F and K were about all there was for 64.5, unless there was a transition model (like a C-coder with a generator and other 64.5 indicators). Resto gurus here could likely elaborate. I own a D-coder.
Maybe he said D but it sounded like E? Or maybe the VIN on the car was obscured so that the F looked like an E? I have a '65 Mustang with a title listing it as a G code but I'm pretty they didn't make a '65 with a Boss 302 engine! *G* The VIN looks like a C to me but some time in the car's past the C suffered a nick.