I've been through GRU a few times in the last couple months. Had seemed remembering seeing flights to AEP out of terminal 3. Quick check of the google says that at least today, the flight to AEP went out of terminal 3, which is the same terminal the AA flight will arrive from.

I did the terminal 3 to terminal 3 transfer about a year and a half ago and do not remember seeing transfer desks where you re-clear security. 80% sure you have to have a boarding pass in hand to get back into terminal 3 without going through immigration.

I would echo the risks of inbound delay. I would also echo the warning that if you do indeed need to go through immigration to check in, getting a braizl visa is expensive ($160 on top of the $160 you wil have to pay argentina) and a pain in the butt to get an appt sometimes...and they will hold onto your passport for upwards of 3 weeks.

Overall, 1h05 is plenty of time if you can get the boarding pass and things go according to plan. I'd put medium odds at best of everything going right though.

Best of luck.