All it needs is a nice Roto-Flex coupling in the drive train, just like in the Lotus Elan....oh! wait a minute...
I'll be contrarian on the cush drive issue, I don't think that additional in-line damping will achieve anything very much. I think that the real problem is that the S&S X-Wedge is a styled engine rather than a thoroughly engineered engine. To illustrate this ask yourself how many other engine manufacturers boast about how heavy they have made the crankshaft? To me the engine is a strange mix of lots of low-down torque that you mustn't use because it will tear itself (and the drive line) apart and no top end because it is too heavy to rev so you actually end up with a motor that has a really rather narrow useable power band.
Having said that, it does look the part, it sounds the part and I think that if as others have suggested you match revs on the way down the gears then you don't have the massive inertial loads going through the drive line trying to spin that massive crankshaft up in an instant when the clutch is dumped. Without those loads the bevel box and the sprockets will have an easier time. At the risk of tempting fate I will add that at 15500 miles I am on the original bevel box which was supplied with the infamous black goo additive (flushed out within 2 weeks of delivery) and the rear sprocket has done all but the first 1100 miles when it was fitted at the instruction of the factory for some unspecified but "known" fault. The sprocket is also one of the early ones that has the belt hanging off to the side - which is another piece of engineering genius; a narrower belt would probably be more fit for purpose! Maybe these things have lasted (so far) because I drive so gently...
The car is enormous fun but does need to be driven around some of its quirks. It certainly is not the thoroughly modern but 1930s styling car that many expected but lies in some strange grey area in between that also plays host to many large idiot grins on the faces of the drivers, passengers, bystanders and from time to time, breakdown truck drivers.
