E&L Instruments Fox 1 Z80 Trainer chip questions

[ROBO5.8]

Hi Folks,

I recently obtained a used E&L Instruments MT-80Z microprocessor trainer. 
My goal is to teach my kids a little about microprocessors.

The trainer has 3 empty IC sockets U1-40 pin, U10-40 pin and U-11-28 pin. 
The parts are missing on the board that contains the keyboard and 7 segment 
displays.  Neither of which work, so I suspect those empty sockets require a 
chip or two for operations.

The parts are probably Zilog or Intel PIO's and a CTC (Counter Clock Timer).

Before I experiment I thought I'd run it up the flag pole and ask if anyone 
can identify what goes in the sockets.

Thanks Robo