Loose heater box?

Hi working on my 67 Barracuda, the bolts are tight out on the firewall where the blower motor sticks out. But from inside the car I can still move the Box somewhat up and down? Is there anything that would cause this I thought the only thing that actually bolted it up was out there on the firewall? Also on the heater controls on the white plastic parts where the cables slips on is there anything that's supposed to go on after the cable is on to secure it?