I am not sure, it could have come like that. My 72 240z (Build date Dec 71) had a unique gearbox mount and was delivered with a 71A box, but had a later 72+ style console.
I've seen option boxes also with the flange attachment (but of the 71B style). So it may be a transitional item for a short period of time, like my 72 gearbox mount.
I have a 71A driveshaft in the garage if you want photos for comparison or measurements?
I would agree with this.
As for non-original motor, it does impact values but to be frank it doesn't determine how enjoyable the car is to drive and an L28 is a popular swap. The biggest factor is rust, although I have a feeling in future a lot more aftermarket panels are going to become available, making more cars feasible for restoration at a lower cost.