Commstar v21/23 modem
A package that consists of an Amstrad modem by Pace and the PACE serial interface.
Pace RS232 Serial Interface with Extra ROM Board
This is a different version of the RS232 shown above, featuring the Serial Interface, but with a separate ROM board below.
This could be modified with 2 pins and a capacitor to work as a x4 ROM box. Pic.4 below shows the modified board.