Curtiss used a single u-joint that is 5/8" 16 spline. The splines don't match but it seems to work for him. His u-joint is the type that is split on one side and clamps on and he probably had to open it up a bit to fit on the 16 mm shaft.
My 5/8" double u-joint is not split and wouldn't fit over the 16 mm shaft until I drilled the splines out.
I used the same thing on the end of the steering column shaft as he did.