Thanks for all the reply! I know what is possible or not possible now.

One more question - if I start a new character, and choose GLA as the starting job, buy a potion to level DRK to 60 and another potion to complete quest up to start of SB, will my character screen show me as a level 1 GLA? I am quite pedantic about this sort of thing. I want this char to be a career DRK.