Sounds like a great gun (and caliber) for your hunt. The 375 has probably taken more elephants than just about any other caliber. And personally, I love a double for hunting elephants; it’s just perfectly made for the situation.
Talk to your PH about shot placement and backup. I personally like the shoulder just below where the ear touches the body. You will drill the heart, and the elephant will be down in 100 yards or less. Hit the lungs and it’s the same thing.
The 375 is also very effective on a brain shot, but the brain is always a tougher shot. If the elephant doesn’t drop to the shot, expect that backup shot. A 375 that doesn’t hit the brain might not be enough to even stun a bull and cause a stumble (the time it takes for the 2nd shot), so just be very ready.
In any case, you will use both barrels. And probably the 2 you quickly reload.
Elephant hunting is awesome. Enjoy it and your double.