I guess I'll have to go count. I was sure that the disc I bought was a 23 spline but then I'm not all THAT good with numbers! I don't know about the S-10's. I actually combined parts from an S-10 unit with a Camero unit to make the one for my pickup. I used the tail shaft from the S-10 to get the linkage in the right place but it meant I had no speedo drive since it came from a vehicle with an electric speedo. The older 3 speeds, the Muncie 4 speed and the Saginaw 4 speeds I have all have a 10 spline inpput shaft.
As you can see from my address I'm from down here in SD but am working for a Co. who's home office is in Westlock. How about that? You may have heard of Lehman Trikes? I head up their Product Support area for US operations.

1964 Chevrolet C-20 Fleetside, Otis
1950 Chevy 1/2-Ton, Kirby
1950 Chevy 1/2-Ton Shortbed, Walter