In the 60’s and 70’s there were many ways to display numeric data. Nixie tubes, Vacuum Florescent Displays (VFD), micro projection systems, you name it. All of them had advantages and d… ...

I just repaired one of those clocks for a friend. It used three 2-digit, 7-segment neon display modules. Not sure if your clock uses the same modules, but I suspect that it does.