This is the chain drive component that he will be using, The kit is available in Australia and is about £750, this does seem a lot of money for something that he doesn't really need but he is adamant that this bike is going to be different from a standard XS1100, this will not only give him a choice of rear wheels but tyres as well.
Please check out the link below of the engineering firm who manufactures this, the kit itself looks very good quality and was apparently used is a race way back 1981 so if it was good enough for a race then this must have been tried and tested and best of all just bolts straight onto the XS1100 engine
HISTORIC CHAIN DRIVE KIT
Credit to Malcolm Pitman who has helped Nordon Pty. Ltd., engineer a chain drive based on Pitman's chain drive conversion. Pitman's chain drive conversion was developed for Greg Pretty's Yamaha XS1100 which he raced in 1981 and won the Coca Cola 800 at Sydney's Oran Park Raceway.
The early model conversion has been re-designed and adapts without change to the standard factory crankcase