In practice, the seats are not interchangeable, especially on the later cars like your 90 with the seat belts mounted next to the center console, not in the center console. The seat belt receivers are such a tight fit in there as is, that the consoles actually become deformed and some break. If you swap the seats such that the seat back rake adjustment knobs are in that space next to the console, the access and fit are just unworkable. But yes, the seats will bolt in on either side.

That said, the upper and lower halves of the seats are interchangeable, and the adjuster is part of the hinge assembly, not the seat frame. If you need to swap out bottoms, you can unbolt the entire seat top with the hinges from the bottom frame. Keep in mind that the driver's side has the quick-release seat height adjustment mechanism and the passenger does not. You can swap that part too.

DS