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I found a couple of old datasheets. There are two packages for that device a PGA and a PLCC, but I did not find a "Ordering" information sheet that said what the part numbering scheme was.
I did find a supplier that apparent has the license to continue building these parts. Rochester Electronics:
http://www.rocelec.com/obsolete-semiconductor-manufacturing/featured-product/?f=ep1810gc-35 So you might want to contact them to see if they have a better idea.
Pete
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Thanks for your help. I'm having a heck of a time finding out what the "AB" calls out. Here is a photo of what I have available.