They make an over running clutch that fits the 1 1/8" spline of the B and then converts to the 1 3/8" that you need. They also make one that has 1 3/8" at both ends. Both probably the same price, so you are going to spend the same money either way you go. I would get the one that adapts the 1 1/8 to the 1 3/8 thus using only one adaptor between your pto shaft and your implement rather that the two ( spline adaptor then over running clutch.
Also I would imagine that if you use both you would really extend the length of you pto shaft before the point where you hook up your implement. I would think that this would put extra pressure on the shaft, but then again I am not an engineer just what I think. I would keep it short.