It seems to me I set one of these radios up as a emergency backup for the local club 30 years ago.
The radio was mine I used as a backup on packet BBS.
I had to go inside the radio and find the squelch gate for the cos. Schematic required.
Or, you might be able to obtain it from the "busy light" when the squelch is open. If it still works.
The audio I think was from the speaker that I padded down to about a line level. since I had the attenuated plug in a 1/8" jack already, but you should probably check that af out pin on the mic plug first. It's likely what you want.
You might run a line from that busy led to the unused pin on the mic to make a clean PNP setup.