[GIZZ]

They do have the internal drum surface machined in to the inside. I'll take full measurements and post it up for reference. I'm thinking about sending the dimensions into maybe Centric and see if they would be so kind as to help out as to what they are from. I seriously doubt these companies are having rotors spec'd and made.

The center bore, unbelievably I used a 3.5" Milwaukee bore saw and the bore is almost exactly that. The axle is like 3.55" so I need to take the rotary file to it today.

I don't like the fact that replacing the rotors in the future will not be easy, I see you will be in the same boat once you are done with your spare set. I'm considering saving up and changing the whole setup which may include the wheels.