The splines is why you need to change the clutch disc,other wise it will not work.
If you are looking at the splines on the input shaft,they need to be cut further back towards the transmission"extended for the clutch disc to travel".
This link use to show a whole lot of possibilities of donor rear ends.Apparently The site was shut down due to billing problems.
rearend donors list Does any stovebolters have this list copied,it's not available through the tech tips section any longer"link is not working".
Tim