What automatic transmission can swap into a 1974 Datsun 620?

I have a 1974 Datsun 620 with the OEM 3 speed A/T. I believe it is a 3N71B model. I noticed that some older Nissan Maximas have a L4N71B which is a 4 speed A/T. Is this something I could more or less swap in to gain an overdrive?