Try a search for "heater core". It has been discussed here before. With the engine out, it may be possible (not sure, though) to access the nut that is on the lower right corner of the heater box. The core comes out from inside the car, but the nuts to fasten it are in the engine compartment.If yo cannot reach it, you may need to loosen the inner fender and reach in thru to the nut. The service manual says to drill out the bolt from inside the car, but they do not say what to do when putting it all back together.