72 duster AC car, heater core removal

Hey guys, I just picked up a 72 duster, the previous owner said he thought the heater core was starting to leak, so he bypassed it. I was going to put a new heater core in just to be safe.

Does anyone have instructions or tips for an AC car? I keep reading how it's a nightmare, but no one has really posted a successful way to knock it out.

Thanks in advance.
Author: scott2683