Got the coupling modified , keyway cut , new spline piece from a later model C welded into it and running into a misalignment issue . Seems like the engine is 1/2" too far forward ??   I need this thing tight to the front pump mount so it's got as much of the splines engaged as possible and utilizes the 3/16" wide key to take the abuse I had machined into the pump shaft (that hurt, btw) . I set the coupling within .030" of the bracket , which is where it sat before although previously