One more thing...and this may (or may not) save you a world of heartburn. My GS550, with only 2,000 miles on it..not bad for 31-years old..had this very disturbing intermittent knock on the top end of the engine once I finally got it running...it sounded exactly like a bad cam bearing...drove me nuts...how could a bike with only 2K miles have a bad cam bearing.
Actually, some of these bikes do have cam bearing issues, but they only crop up when you get past the 30K mark...was this a premature example?
I would take the tank off to fully expose the top end, set up a gasoline IV line, start the bike, and nothing..ran like a turbine. After I reassembled everything, every now and then I'd get that tapping, which would have me pulled over on the side of the road with a big neon question mark hovering over my head.
Turns out it was the vaccum fuel valve, fluttering at a certain RPM, and it was amplified when the tank was partially full...of course, when I had the tank off, I'd never hear that noise.
Anyway, I installed a $15 fuel valve rebuild kit and that sound of doom went away.
You may never need this information, but if you do get a weird sound...this might help...the few GS550 owners around need to stick together...