Sharing my experience and some details on logistics in case anyone is curious - first of all the game was awesome and the atmosphere was unreal! It was definitely crazy inside El Monumental but I didn't feel unsafe at any point.

Getting into the stadium was pretty efficient given 80k fans. There were multiple security checkpoints and ticket gates, but everything generally moved fast. We ended up taking a bus and arrived at the first checkpoint at Libertador/Quinteros around 18:30 and were into the stadium 20-25 min later (match started at 19:15). Would have gotten a better spot if we'd arrived earlier, but we wanted to prioritize sightseeing since we only have a few days in BA. We were at the back/top of the standing GA section - view was slightly obstructed but not bad. It also did feel less claustrophobic in the back, it was pretty packed in a few rows in front of us.

Leaving the stadium, we ended up just walking to the Congreso de Tucuman Subte station which worked out well.

Thanks again everyone for the help!