Hi guys
Does anyone know if the 79 model Datsun sunny shares the same engine, gearbox, tailshaft as the 120y or the 1200, and can the parts be mounted in any of these two cars?

It depends.

The engines are bolt-ins between the B210 (74-78 Sunny) and B310 (79-82 Sunny). The B110 (1971-1973) engines use different mounts, so it's not strictly a bolt-in. See Engine Swap article.

Aussie B210 sedans used a different differential, so the tailshafts are different.

B310s used either 56 or 60 series transmissions. B210s used 56, 60 or 63. All the A12 engines, regardless of year, used a 56-series tranmission, so those are direct bolt-ins. The 60 interchanges with the 56 with some fabrication. Read this: 5-speed Overview for information on transmission swapping.