When i used to fit these systems i seem to remember that the pipes were actually numbered at the silencer end 1, 2, 3, & 4 to help you get them in the right place. Like all good mechanics i only noticed this AFTER sruggling to get it right!! Also to the best of my memory the only difference in any of the 500/550 sets is the silencer mounting bracket as the rear footrest is in different places on different models
Now when fitting ALWAYS use new crush gaskets at the head end or i guarantee you it will leak!!