bigger rear disc in rear than front a problem I assume?

Have you asked @HemiDenny? I'm sure he has an idea of what some of his customers are running for brakes and wheels.

The other thing is, I don't think the Wilwood hubs will clear the factory cop wheels to begin with, regardless of the rotor size. The hubs used with the Mopar Wilwood kit definitely won't, the hub diameter is significantly larger than the hub bore on the cop wheels. Not sure about the MII kit. Do you have the part # for the Wilwood kits that you want to use?
I have wilwoods all the way around on my car, the cop wheels fit. Not sure if this helps you sense you posted this in Nov

IMG_1403.jpeg