American is out of terminal C and Silver was out of B. If the ticket is booked on one PNR it’s likely they will get you to the connection. Might even pick you up at the arrival gate since all paperwork would have been checked in ORD. They would likely hold the bus a few minutes to get you on. If it’s two separate tickets all bets are off and at 30 minutes prior they cancel no shows and put standbys on. Gates are not assigned based on connecting flights as connections are different and every arriving American flight from the US will have connections.