swapping steering column shaft/rod

I'm swapping my 68 Dart column shift for a 68 Dart floor shift column. I just found out one is shorter than the other. So I want to put the shaft from the column shift unit into the column of the floor shift unit. So I dismantle form the wheel down? Also, where the shaft enters the column at the bottom, there's a white plastic bushing. Is this pressed in? What do I have to do to actuall free the shaft from the column?

Thanks