EY looks like the A346 is for the first three weeks of Nov.
They have F class, yes, but are a reduction of 20% in J and nearly 30% Y capacity.
Yes, the 3 class A346 has 292 seats, the 2 class B777 has 412 and the A332 has 254 or 262 seats according to seat guru.
Not sure what determines when QR use the A333, whether it's just availability of a/c or higher advance bookings for certain flights.