I've replaced cores on both my '83, and '84. The '83 has A/C.

Both cores cost me around $25 at the local stores.

There are other topic threads here that go into detail what has to be done. The A/C version is easier to do, IMHO...

After you change the core, everytime you turn the heater on, you will feel kinda warm inside, because you know that YOU did it yourself, and didn't have to pay someone else.

I really like that feeling.