I had to debate how to deal about wheels. The Jeep Grand Cherokee wheels that I have, have a fairly small center bore. I could bore the wheel out to fit the GMT400 brakes, or I could turn the hub down to fit the wheels.
I tried opening up the wheel center using some stacked hole saws and a wrist-breaker drill (I do not have a lathe than can spin an 18" wheel), but it went awful, and likely couldn't be balanced since the center was no longer true. That was a dumb idea. I don't know who thought that up, but what were they thinking?! I won't do that again (but I did correct the wheel center to be true again)
The cut-to-length 9" axle shafts I ordered from
East Coast Gear Supply have a hub diameter that is smaller than the Jeep wheels, so I cut the front hubs down to match the axle shafts.
In theory, once these hub/rotors are no good, I'll machine the rotor off, and use Grand Cherokee SRT8 rotors for a big brake upgrade. It works in my head, dunno if it will work in real life.