You can piece a system together. The issue becomes the caliper bracket. They don't make one. The hubs are close enough to use on the factory disc spindles so you'd have your choice of rotors.
I ditched the factory rotors, machined some '14 MKZ rotors to fit. Then I made caliper brackets on the mill out of aluminum. I use their Dynalite forged calipers factory booster and master.
Just the front calibers and rotorsWhat system are you looking to "upgrade"?
Wilwood doesn't have a suitable kit for a car as heavy as a Cbody IMHO. None of their rotors are as thick as a factory 69-73 11.75 rotor at 1.25" thick.
If you are talking about a Budd system, there is a procedure to install a Supra rotor that any competent machinist should be able to accomplish for much less than an aftermarket kit.
Mike Pittinaro's Supra Rotor Conversion for (Chrysler) Imperial Budd Brakes