The factory went to the 60 series gearbox when the a14 engine was installed, & later, the A15. This was because they felt that this gearbox would survive well beyond the warranty period, so they obviously didn't think that the smaller 56 series box would provide the desired level of reliability in every case.

In reality, it's not really the engine so much that will break the gearbox, it's the DRIVER. If you give it a hard enough flogging, then you will break the 56 series gearbox with a stock 1200, but if you drive the gearbox with a suitable measure of respect & reverence, even with an A15, it can outlast the car.
So,... what's your driving style.