Datsun 1000's & earlier 1200's used the Jatco 3N71A, but later 1200's & all later models used the 3N71B like this one.

It was really overkill for these smaller models as this same basic trans was used in the big 4's & even the 6 cylinder models.

This is why I believe that the 4N71B will bolt to the 1200's bellhousing, use a 1200 torque converter & can be made to work behind an A15 in a 1200 car.