Man, Oh Man

I have this grognardy nostalgia for dual-classing and multi-classing (double or even triple) the way it was in second edition. Or some similar method. Split my XP evenly between both of my classes? Okay! Have one class that stinks (thief) but only takes half the XP of the other class (wizard or paladin) so it's still keeping pace with some of the other party members? Great! Not balanced per se? Relying on delayed gratification for a superior power level payoff? Fine with me!