For those of you who want to know how to make your 87 trans in to a 88-90 trans with the closer ratio 3rd & 4th.
Here is what you do: Change the 4th driven gear to part #: 24341-43B10. It is item 22 on the trans fiche just MAKE SURE YOU GET THE 22 TOOTH GEAR, NOT THE 21 TOOTH.
Also you do NOT need to purchase the 4th drive gear i counted mine right out of the cases and it is a 20 tooth, the exact same for all years, 87-90.
In fact a neat trick to do (thanks to Mr. Dale Fry) is to switch out the 4th driven so 3rd & 4th are close ratio and leave 5th the taller gear so you get the best of both worlds lots of torque to pull 4th gear on the hill and high top speed on the flats in 5th.