The T40 and T50 gearbox's look identicle. Infact, its posiable to get a T40 gearbox, buy some parts, and convert it to a 5 speed T50. This is what they used to do in the USA, but I havn't heard of T40 gearbox's being used in Australia.
The K40/K50 gearbox is very different, and is only gor #K motors.