HmmÖ suspicious amp.
With the S/N filed off, it must have been stolen at one time or sold through a shady store that was not a Fender authorized dealer. (I have known of stores that got their new merchandise on the black market and then hid the trail by removing the serial numbers. How they still found buyers is beyond me)
The Fender Field Guide must have a typo or you misread it. There were no SF amps in 1964. Your guess that it is a '73 or '74 a good bet.
ALL the pots are new. Thatís strange.
Tube chart missing. There was no date coding on the SF amp tube charts anyway.