I found a driveshaft site online called Denny's Driveshaft. They sell a 16 spline yoke but can't build a driveshaft with that because they can't balance it with that 16 spline yoke.

I used their diagram B for measuring. https://www.dennysdriveshaft.com/app/webroot/img/File/how_to_measure_diagrams/b.html

#B6 came in at 56.625"
#B7 = .375"
#B10 = 3.129
#B11 = 1.062

If this sounds the same as a production shaft that would be good. Could use help finding a driveshaft. Let me know if you have some good suppliers.

Thanks again.