Damn that is some advanced Atari $#@%! You been busy going retro. I did not get much past pong with my first set and they are not even showing it here https://www.idealine.info/portfolio/library/pages/tx-games.html. Maybe the Chess is worth the battle.

Seems all setup to do 300 baud talking with CompuServe..think you can find it all there. And yes had RS232 memorized and could solder a 4k or 16k (going big here) on a motherboard for you without issue if you needed some hardware interventions on top of things.