If it turns out that this is a real problem and that, looking into the future, chains of adequate quality are likely to become unavailable then there is another solution. That is to replace the whole of the chain and sprocket or belt arrangement with three spur gears. One on the engine main shaft, one (an idler) on a pivot supported in the tunnel provided for a left hand kick starter shaft and the third acting as the base for mounting the clutch. If you look at the system on some Japanese bikes they drive their gearboxes via a helical gear on the engine output shaft and a larger helical gear on the gearbox main shaft (no intermediate idler). The clutch is mounted onto this gear via a plate with two sets of springs, one to take the drive forces and the other to take the overrun forces. This is the same idea as most cars. The springs replace the E.S.A. Nothing to wear out except gears and a wonderful ready made interface for a starter motor mounted where the dynamo normally resides, or, drive the central idler gear via a shaft that goes all the way through to the kick start cover and use a modification of the French starter system to drive this shaft, but this time please, with a Bendix or pre-engagement system.