The 88-90 trans has the closer ratio 4th & 5th than the 87.

Now if you look at tooth count the 4th drive or driven has the same tooth count but if you mic it the diameter is different so you need both the drive & driven to swap the gears out.

Another trick I learned from the fisherman is to only swap out 4th, making 3rd & 4th closer ratio but leave the 87 5th so it's taller and you can go faster on the top end.  this is how mine is and when I get in to 5th and the pipes lit it'll boogie