This might be a good next project for Brent. HD used to have a spring loaded engine sprocket on the primary. There was an inner part that was splined to the crankshaft and an outer part that had the sprocket. the two were sandwiched together with cam faces and held down by a heavy duty spring. The cam faces would allow the outer bit to force against the spring and absorb driveline shock.
It should be possible to make something like this to fit the output shaft of the Triumph transmission and eliminate that rubbery thing.
