Will they fit = Yes
Will it be easy to mount them = No
89-91 seats were built for the door mounted seatbelt arangement, and the floor mounting points changed. You might be able to get them to work though, just be prepared for some fussing. Seat swaps are hard! I've done a couple myself already - 90 DX seats into my 1g Si, 92 Prelude seats into my DX