Smallest rotor I see is an 11" rotor and by the time you stack a caliper on it you need over 13" of clearance or the rim rubs the caliper. I can't find one, but you would need a kit with a 10" rotor at the largest and I think that would be a tight fit. After that we have to think about how much cooling will the rotor will actually see sitting in that rim with a backing plate.

 

Not sure about fitment on your spindle but the 76 Mustang II rotor is a 4 lug 4.25 bolt circle and is 9.3" in diameter. Would fit under a 13" wheel if the wheel will clear the caliper.

Specs
# of Bolts: 4
Bolt Circle Diameter: 4.25 in.
Brake Rotor Diameter: 9.3 in.
Brake Rotor Discard Thickness: .81 in.
Brake Rotor Thickness New: .88 in.
Brake Rotor Type: Disc Brake Rotor And Hub
Height: 3.91 in.

Another option is to go with a larger wheel like these from Summit Racing.

4 lug 14" wheel

 

Drum brakes

Ceramic will take a lot of heat and work just fine on a 6, You can buy kits pretty cheap.

 

Thank you all for great feedback. Awesome community out there!