Some of the Railking Diesels are NOT O scale. Some of Those are the SW1, Sw8/Sw9, Sw1500, MP15 as thier hoods are too wide and a bit too high like comparing Lionel Postwar NW2 to the Scale NW2.
NOte the Later Railking diesels made in the last few years have More detail that rival Premier diesels at a reduced price than Premier.