The silencer is (I believe) Yoshimura, but now in the bin as it had been drilled, painted over peeled chrome, and corroded. Don't know about the pipes - they were also badly corroded, not sure if they are useable or not. I know very little of the bike's history - it was given to a friend of mine in exchange for work owed and before that it had sat under a tarp in a back garden for about 17 years. The frame was registered in 1977, but the engine is a 1974 K4 American motor, so I am guessing that a US import was used as a donor bike at some point. That would explain the Abe wheels (which nobody over here seems to have heard of) and also the Abe 812 big bore.
It also has with it a hideous bright red home-made tank which looks like Herman Munster's head and a very 'early GSX Suzuki' inspired seat/tail unit which is equally worrying. Personally I favour a CR750-esque look, but I have to find somewhere for an oil tank as Tony Foale does not favour using the oil in frame as apparently it can cause feed problems - so if he tells me that and for what the engine is costing, who am I to disagree? Also want to show off the monoshock, so will try to get a fuel tank with an oil compartment built in. That's the plan, but anything can change.