SBP Disc rotor ?

I bought a used, factory sbp disc brake setup for my Dart, and was tearing the parts apart from the spindles. I ordered a set of replacement rotors, and just picked them up, but they're just the rotor, without the hub assembly. So, do I have to press the old hub assy. off the original rotors and re-use them on the new rotor, or did I get the wrong rotors? The service manual makes no mention of separating the hub from the rotor. Thanks.