Heater box removal

[KyFarm]

Well the secret disappearing coolant has been solved. I have a leaking heater core.

I was told by a friend that I could get it out through the inside of the truck, Nope. So I began removing the heater box holding the core to the firewall. Got down to the last bolt and I am stuck.

How do you get to the bottom far left (under the blower motor) bolt holding the heater box to the firewall out?

There has to be some secret other than removing the entire wheel well hopefully because the bolts holding that to the front quarter panel turn but don't come lose.

I tried all my extensions and knuckle drives and I just cannot get to it. Any help is greatly appreciated.

truck is a '69 K10