You have to tear out the dash board of the car to find where it's located exactly, then you can remove it, other than that I just bypassed mine, under the hood are the hoses that connect to the heater core.
I dont know if this is true on yours, but on my 77 Impala the heater core is under the hood on the back passanger side near the AC hose connections. I had to remove the fan and unmount the upper half of the cabinet (quite a few screws, some up near the window wiper). With this removed I could then remove the heater core. Took my about 3 hours and on a scale of 1-10 on how hard to do with 10 being hardest I would say a 3.