I don't recall if TA's were available with AC or not so I don't know if your car is AC or non AC. My 'Cuda is a non AC car and removing the heater core is fairly easy. There are three nuts on the firewall side from the blower motor and one inside by the fresh air intake from the cowl. There are three cables, two from the heater control and one for the fresh air floor vent. It will help if you remove the clove box to gain access. There is also an electrical connection for the blower motor. Before removing the heater box blow the water out through the heater hoses to minimize the mess inside the car. As for new cores, I am not all that impressed with the quality. I put a new one in my car and it started to seep about 2-3 years after I put it in. I've got a bottle of Bars stop leak in it now and it's holding, but next Spring I'll break down and put another new one in and keep my fingers crossed.
If your car has AC it will be significantly more involved. Besides the AC lines the heater/AC box is bigger and heavier and probably has vacuum lines and more electrical connections. The cost of the heater cores for either one should be similar and under $100.00. Good luck.