Freezing Balls

I know you guys have all the answers so hopefully one of you can help. I'm replacing the heater core in My 77'Z28 but i've run in to a little problem I don't know what I'm doing. Chilton's and hays manuals don't tell me sh**. Ive pulled the glove box the air directon duct and every think else that seemed to be in my way, still the black plastic box won't come out. WHAT AM I DOING WRONG?!?!? Chilton's says that models with A/C should only be done by a qualified Tech but I don't have that kinda money help me please before freeze to death.

u have to remove the inner fender and go in from there
book time on this job is 5-8 hrs

You have to go in from the inner fender ont he firewall. Unscrew the heater box from the firewall and everything should come out. I'm not sure what difference there is w/ A/C.

Not a fun job either way.