How can I interface bare glass LCD to an arduino?
When I disassembled my Casio FX-85GT, I found that there were two main chips (both under epoxy blobs): what looked like a microcontroller, and a display controller. The display controller would drive the LCD directly. Unfortunately, driving a 128x64 pixel display without a dedicated driver will be next to impossible. A cheap solution is buying a ready-made display with a controller, e.g. this one from SeeedStudio.

I don't know about the 991es, but if it is just a character display you are after, they are even cheaper.