All the drums were 11" on C bodies in '65, but there were 2 widths on the fronts and 3 different widths on the rears depending upon certain options.
When I say width, I'm talking the width of the shoes and the drum's inner contact surface here - the measurement is of the shoe's width
I'm just going by memory here and there are others who I ask to correct me if I get things wrong:
Fronts varied from 2.75" wide (Standard front width for most cars - from 6 cylinder up to 383 2 barrel equipped cars)
&
3.00" wide (Police, Taxi, Fleet and other heavy duty optional packages like trailer tow or mountainous locations)
Rears varied from 2.00" wide up to 3.00" wide.
Most 3.00" front drums were paired with 3.00" rear drums.
Also, the 3.00" package typically did NOT come with automatic self adjusters, but many people installed them as the automatic ones were easily swapped into place with the non-automatic adjusters.
It's very unlikely a 318 automatic car would have anything but 2.75" fronts and 2.0" (or 2.25" - can't remember) rear drums unless specifically optioned for the 3.00" heavy duty brake package.
There was the first year of front discs, but they were police only until '66.