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I assume it is cross drilled and floating but not "vented"? Vented usually refers to two braking surfaces separated by radial webs between them, allowing for air flow for cooling. 

Have heard that original type Norton rotors can need to be test fit against hub and rotated to other bolt alignments to get best flatness to hub.

With floating rotors, sometimes the spindles are too stiff to allow proper centering. Try manually moving disc at each spindle to work them a bit.

Also heard some Lockheed calipers and rub on the floating Girling type rotors and need a little clearancing where the spindles rub.