Maybe my stuff was mixed around before I got it. I have been rebuilding a race motor. It is in a replacement case so I cannot accurately place the innards in the timeline. It has the longer, late final drive shaft. It sat for years in a partially rebuilt state. It had been cleaned at one point, but did not have oil in it. There is some bad spots on the gears, so I had planned on replacing them, actually the entire shafts from my parts motor. The parts motor is #CB750E-2530036. The # places it as a 76F motor. My transmission shafts match up perfectly from one motor to the other. This is the bottom shaft from my big motor meshed up to the top shaft of the 76. From your post, this is correct. What I don't get is that the final drive shaft is different. The one on the left is the 76. But the two gears are exactly the same.

The 75K final drive gear that Kayjohn has is a different ratio than the 78K. Is the inside of the gear, where it slides onto the shaft different as well? I don't understand why if the 75 final drive gear is used on the 78 output shaft, that it will not mesh with the 75 transmission shaft.