Thanks for the advice guys.

>From what I have found so far for my year and model car, if a copper
core is available, it is only available for cars without air
conditioning, and an aluminum core is availbale for cars with air
conditioning (my has air).

I was going to go with a core from the local NAPA store, but their
price (under $30) had me wondering about the quality. I'm considering
just buying an AC/Delco core for $80 and being done with it..