When improved gears were introduced in A+ transmissions starting in 1979, the primary gear was also revised. It is identifiable by have 29 teeth. Bushing IDs are 1.629" and 1.504", front and rear respectively. The front bush is the floating design and is held in by a circlip. The oil slinger ring has been omitted.
If you are fitting an A+ transmission, you must use the corresponding A+ primary gear and drop gears.