Heater/AC removal HELP!

[Jamie DeRienzo]

I am trying to remove the bottom part of the heater/AC unit out of my 81 2.0L Beta Coupe. I have the front half separated about 1-2 inches with all the clips off that I can find. The only thing that I can still feel is what feels to be an 8mm nut at the back. First question, what the heck can hold this thing on? The nut feels like it doesn't attach to anything and I'm sure from the tugging I've done the screw would have broken the plastic if it were what was holding on the bottom part of the unit. Any advice is GREATLY appreciated. I'm totally stuck now... -Jamie