Also, I would indeed be curious as to where you’re tapping the COS line inside the RT85. Simple enough to use pin 2 of the DB-9 connector on the DRA-30. And if there are three contacts on the audio jack of the radio it would be easy to disconnect the existing radio circuit from its “ring” contact and re-purpose it for the COS. The 2.5mm audio cable I’m using is a 3-foot cable I purchased on Amazon and cut it in half. My DB-9 plug is actually a breakout plug making the use of the terminal blocks a great alternative to soldering. As for working on SMT circuit boards I got very good at replacing 168-pin fine-pitch “chips” using a 1/64" solder tip, solder paste and a 10x jeweler’s loupe.