The Preferred buildings are the 1960's area. They are the closest buildings to Classic Hall which is the lobby, food court, and bus stop. Because of thier convenience, they are $10 extra per day per room.
If you have paid for the Preferred section, you are guaranteed a room in the 1960s, no request required. CRO should not have let you request the 1970s section, since they are not preferred buildings.
If you switch to a non-preferred building, you can request the 1970s, but you will not be guaranteed any specific decade, especially by checking in late at night.
My advice would be to keep your Preferred reservation, and stay in the 1960s. One thing to note... Half of our rooms are connecting, so that shouldn't be a problem to get, but there are only a limited amount of rooms with a king bed. It should also be noted that some of the king bed rooms will have a disability accessible shower (basically, just a standard shower, no tub) instead of a standard tub/shower combo. All of the double rooms will have the standard tub/shower combo.