I bought a new complete system from David Silvers Spares, the muffler seems a genuine Honda item evidenced by the stamping, although I will have to take their word on the downpipes and collector.
Doing a trial assembly before fitting to the bike, the system doesn't seem quite right where the muffler connects to the collector - the overlap of the two pipes where the muffler slides over the collector pipe seems inadequate and the clamp doesn't appear to clamp anything together, it just clamps onto the pipe from the collector but doesn't overlap onto the muffler. The other problem is that the packing is so wide that there is no room to fit the muffler onto the collector pipe other than by siding it inside the packing, but the fit is impossibly tight. I have already ruined one packing attempting this, and note that it is virtually impossible to cut the packing due to the steel mesh inside it.
The last photo shows the exit pipe from collector with the packing and clamps. The external clamp will not fit over the front end of the muffler, so it can't actually clamp the two together, all it does is clamp the packing to the pipe. The packing is a tight fit and it seems impossible to slide the front end of the muffler inside / underneath the packing.
The muffler is mounted securely to the frame by two bolts, but the downpipes and collector are only held by the top end clamps onto the cylinders. The connection between the collector and the mufffler seems to provide no real security at all.
Would appreciate any advice or guidance on how this system goes together.