The missing spline is normal in later yoke versions, to allow any fluid to escape on compression without creating hydro-lock. Earlier versions used a multi-lip seal on the output shaft, riding in a smooth-bore section of the yoke. Perhaps that seal is what you are running into, but it's more than 1.25" down the shaft. A close inspection of both parts should reveal what's interfering, from seals to bent or damaged splines, and so on.
A pic from my parts bin of the seal the early yokes used: