Trying to piece together a trans out of a box of parts that I bought. I am not sure how to tell the difference between a 1987 and a 1988 to 1990 4th drive gear. The tooth number is the same on both at 20. According to the sticky post of engine changes it just says that 4th drive gear is a different size. Can anyone tell me how to positively ID the year of my 4th drive gears? All the other gears can easily be figured out by counting the teeth. Thanks.