Oops. I thought one of my Fastbacks had the indentation. I had two other San Jose Fastbacks (both built in mid 66), but they were sold BDC (Before Digital Cameras).
Pic 1 - 1965 (May 11) San Jose GT Fastback - 5R09A219xxx
Pic 2 - 1966 (Oct 18) San Jose GT Fastback - 6R09K121xxx
Pic 3 - 1966 (Oct 15) San Jose Hardtop - 6R07A120xxx
Note the distance differences between the spare wheel mounting bracket and the forward body clearance in pictures 2 and 3. There is more distance for Hardtops and (I assume convertibles) than for a Fastback, but the distance from the spare mounting bracket to the wheel housing is the same for all 65-66 body styles.
I assumed that the dent should be there because without it the spare doesnt fit flat on the floor and line up with the hold down clamp.
Keep in mind that the standard jack and jack handle were placed under the spare for storage which would "level out" the wheel.
The spare in my 65 Fastback is a P195/75R14 and it fits "tight" on its front edge against the inside surface of the wheel housing. It could have used the indentation.
Jim