The 2708 is not an easy EPROM to use. It requires -5V, +5V and +12V and most programmers can not handle it.
Elektor published an article how to use a 2716 instead of a 2708 (eliminating also the need for -5V and easier programming).
ROM in 2732
But an even more common 2732 EPROM can be used instead of the 2708 EPROM when you perform the following:
– cut the traces +12 and -5V
– K6 to the VIA,
– K7 to the EPROM.but leave K7 to the 7401 intact for the STEP function.
– /CS from VIA to K3 to move the VIA to page 0E (jumps in the EPROM are adapted for that)
– /OE from the 2732 to ground
– A10 and A11 of the 2732 to the addressbus
– /CS from the 2732 via an inverter to A12, note that there are two unused ports in the 7402 with grounded inputs: cut those! and add a pull up resistor.