The frames are pretty mutch the same, bar the rear footrest hangers changed on later 550's so most parts including mudguards are interchangeable in practical terms though at some point the rear light mounting changed too. You may need to drill some holes for the lights depending on the year of 550 or use a 550 light brackett. Apparently the 400/4 guard fits too (several people told me the guard on my 500/4 was off the 400) there are fiberglass pattern guards around on ebay which might not be as pretty as the chrome jobbies but last longer. I've fitted one of these and put the useable chrome guards in my spares corner. I've even got one with the original waring/tyre pressure stickers! seems too good to let get more pitted.
