Yes. It is a direct fit. Nissan didn't change the rear hatch and they are interchangeable. 1984-86 won't have the third brake light. 1987-1989 will and you'll have to wire that in if you want it to be operable.
No. Not without custom brackets. If your gonna put Z32 seats in a Z31 I would spend the money on a nice Recaro racing seat, or other aftermarket seat. Good quality company's like Recaro will make the brackets for the seat to bolt right in. And they look good too.