Welcome to LTG! Yes that serial number is from 1966. The Starfire truss rod cover was most probably added later on, but as Smiert said, that is no problem, the original metal truss rod cover loooked the same sans the Starfire script on it. And the Starfire was based on the T-100 anyway.
The 1966 and 1967 catalogs showed an older T-100 model with single coil Franz pickups and older lip top headstock. Only the 1968 catalog started showing the newer model like your 1966 one. The difference in that 1968 catalog photo is that the Chesterfield logo was already added to the headstock which the 1966 model did not have yet. The text in the catalog also has errors as it describes the older "Franz" singlecoil pickup whereas the so called Guild Mickey Mouse pickup in your guitar (and in the catalog picture) has no individual string adjustment screws.
Hope that helps!
Ralf