Where did you ever get the idea that the rear splines would be 24 or 26?

The only output shaft spline counts I ever remember seeing for any Ford transmission were 25, 28, and 31. C4s have 28.

You will need to find a 28 spline yoke that will fit your C4 tail housing. You may be able to simply replace your current yoke if the U-joint is the same. Otherwise you have two options. First, find an offset U-joint that will connect the two, but that is not a likely solution. Or, take your driveline and new yoke to your local driveline service center and have them make the needed modifications to make it fit, usually costing around $150.

______________________________________
mmerlinn (http://mmerlinn.com) -- "Careless and sloppy writers are usually also careless and sloppy at thinking. Answering questions for careless and sloppy thinkers is not rewarding." - Eric Raymond