The bearings come in two parts, basically. For the sake of description we'll call the two parts "rollers" and "race." The "race" is the part that the rollers fit into, and they are usually mounted in the rotor hub. If they are not pulled out during a bearing job, you are using "old" races with "new" rollers. I think Scott is advising you to pull the old races, too.
Just to qualify: I don't have a 68 Firebird. I haven't done the bearings on my 69 Firebird. I am quoting from my GTO experience.
