This is incorrect - the gates at T1 in MEX only go up to 36A. You are right in saying, however, that the gate area will be very busy, though not necessarily with other European flights. American and some of the other Latin American carriers usually use that 29-36A gate area.

BA usually use gate 31, as the stand it is connected to is one of the few able to accommodate the 747 at T1. However, it does sometimes use the other widebody stands, especially if the inbound BA243 is delayed or is scheduled to arrive much later than the other European widebodies.