This question already has an answer here:
I booked a flight from BOM (India) to CPT (Cape Town) with a lay-over at DOH (Qatar) using Qatar Airways. The flight numbers are QR 557 and QR 1369. While making the booking, there is an option of seat-selection which I used, the seats were shown in 3-4-3 configuration. I did see that on the Qatar Airways Wikipedia page that they have both Boeing and Airbus but just like trains, I am guessing there would be the same aircraft which flies the same route. The first hop is a short-haul 3 hour flight while the next one is biggie 9 hour long-haul flight. I also believe this is routinized to a large degree as you need to have the staff, captain and the ground staff intimately familiar with the aircraft for taxing purpose, weight issues (as I read in some other thread) hence would make sense to have familiar aircraft.
I would understand if there is now secrecy about these sort of facts as terrorists knew which airplanes they were on and did take training before doing what they did on 9/11.