Why not just use patch points? Wire it to a couple of TT connectors.
You could possibly use the 237 card. The 2 balanced output hybrids H1 and H2 feed a balanced output to connector conn2.
These are present but not used on my console.
Left goes to pins 3 + 7, Right goes to pins 4 + 8. Looking at the 237 pcb with the label on the bottom right the bottom right pin on conn2
is pin one. The top right pin is pin 4. So, the 4 pins in the top right corner of conn2. You can buy the female pins that fit conn2 at Newark PN SC 16ML1S6.