changing heater core 1977 C10

Hello, i have a 1977 Chevy c10, 2WD with a 350. Just wondering if anyone has ever changed a heater core in one of these and what is involved? Are you able to get access to the heater core from under the dash or do you have to take the entire dash apart? Hope somebody can give me a few tips before i start in and end up doing a bunch of useless stuff. Thanks in advance for any help you can give,

Steve