On the Australian B310 Sunny's firewall, you will find a tag like this & it reveals all that you want to know.
This one is a wagon [WPB310]
The engine [A15[S]] is obvousuly an A15 with the "S" telling us that it has a 'staged' [progressive] 2bbl carb
The trans [F4W60L] is a floor shifted [F] four speed[4] wide ratio [W] sixty series [60] with the long [L] extension housing while the diff [HB37] is a second generation H150 unit [HB] with a 3.7 to 1 ratio [37]

You don't even need to get your hands dirty when trying to identify what components were fitted as original equipment to many Datsun models from the late 70's
Thanks very much to Feral for providing the info in the first instance.