Quadrajet was not used on the 428 Cobrajet.
I had a 1969 Torino/Fairlane Cobra with a 428 Cobrajet and it definitely had a Holley carburetor (weird size, 730 CFM, IIRC). I got mine in '71, and I know the previous owner. It always had a Holley, and I have never seen an article that mentioned any other brand of carburetor.
Super Cobrajet 428 was part of an upgrade option on Torino's and Mustangs. The package added an engine oil cooler, upgraded connecting rods and crankshaft, and an upgraded intake. It was delivered as part of the Drag Pack option, which also included either 3.91 gears and Traction Lock, or 4.30 gears and a Detroit Locker. It had the same (underrated) horsepower.