Pins 2, 4, 5 would be the physical pins on the DB-25, as they are referenced to in the CPS (GPIO Physical Pins).
Using DB-25 Pin 7 for receiver audio, and Pin 13 for transmit audio.
Pin 13 “should” go straight to the modulator (in theory), allowing you to send PL, without it getting filtered/processed out.
Just pulled my cable apart, and confirmed those are the pins in use.
Lee