I'm about 10 years late to this thread but I decided to upgrade my tuners on my Fender Classic Series '65 Mustang. This is my exact model:
There were a lot of various models of locking tuners thrown around in this discussion, and after my best attempt to research what would literally "Drop in" – the one that I think best fits this series of reissue Mustang is the Kluson 6-In-Line Locking Revolution Series F-Mount Tuners - sold by Stew Mac (product link).
The issue I have with the other tuners mentioned here (Gotoh, etc.) is the positioning of the screw mounts on the back of the headstock. My Mustang's stock tuners have 2 screws on each tuner placed diagonally from each other – and this model of Kulson is the only one I have found that matches that screw pattern.
If anyone has experience with the Kluson 6-In-Line Locking Revolution Series F-Mount Tuners please let me know. Like the original poster, I don't want to drill any extra holes in my headstock or have to retro-fit a new locking tuner to work here – I just want a dependable, locking tuner that fits this model guitar no muss, no fuss. I will be ordering these & will post my findings soon. Thanks!