I had to replace my heater core in my 79 (with A/C), new core ran about $40.00. In order to get to the heater core (and blower motor), you will have to go in through the dash, passanger side, under the glove box. You will have to remove the glove box door, glove box, A/C box cover, various ducts and hoses to get into the actual box and core. It was not hard, just time consuming and if you can remove the seat, it will help with more room. The hardest part was removing the old hoses from the heater core, Since I was replacing the hoses, I just cut them off. If you replace the hoses at the same time, take note as to which hose (in/out, upper/lower) has the heater valve and direction the valve goes. If you get it backwards, you will have no heat. Be careful putting the hoses back on so you don't crack or break the fittings. I always wet the insides of the hoses with water so they slide on easier. When you tighten the clamps, be careful not to crush or distort the tubes as they will leak. Might as well check the blower motor while you're at it, as it will be right there. Your A/C cooling coil is also in this box as well and I can't remember if it was in the way or not. Mine had been disconnected, so I pulled it out and pitched in the trash.