If you use the 69 drum spindles all you have to do to compensate for the bump steer is use a set of baer tracker tie rod ends or bumpsteer correction kit from pro motorsport(dr gas) I believe.
The 69 Drum Spindle is a C6OA Spindle. This was used first on the 66 Fairlane V8 Cars, then on all 67 Mustangs, Fairlanes, Comet, Cougar, etc, then on ALL Drum brake 68 69's--All Drum Brake 6 cylinder, and V8.
As You stated, if proper alignment, parts are used, these are excellent spindles to use in the 65 66 conversion, are FoMoCo parts, use the Mustang Tie Rods, Fit the Mustang wheels, Fit the Bigger rotor, etc.
Bolt on the K/H 4 Piston per caliper Disc Brakes, you got Big Brakes, and are Mustang, Fairlane style.
Much better selection than jumping through all the hoops fitting the Granada brakes.
Dan @ Chockostang