Hi there.
A datsun gearbox that has 56A stamped onto the bellhousing, usually is a four speed out of a 1200, 120y or Sunny that use the A series motor.
There were 3 types of 5 speed gearboxes that were used with the A series.
1: 5 speed non-overdrive, close ratio, 56 series. (ribbed bellhousing)
2: 5 speed with over-drive, dogleg or non-dogleg, 60 series.(60/60A was non-dogleg)
(60/60L was the dogleg)
( smooth bellhousing).
3:5 speed ( used on L series motors, but some were used on A series) (large gearbox, dogleg shifter)
The first two were probably the most common types.
But any 5 speed gearbox for an A series are very rare nowdays.