Wonder what their donor rotors are. Unsure if the rotor picture in the first link is representative or not, but it's a 6 lug re-drilled for 6 more.
Just FYI for the OP, the later disk calipers from Cadillacs use a thinner rotor, I believe someone found a GM pattern 6 lug rotor thin enough to work with those calipers, used on the newer trucks (88+ somewhere) that was the right thickness. Might be hard to find the post, but there should be at least one covering 14SF disk conversions that lists the rotor application.