I saw a guy that had a stock 550F tank chromed. I wanted to ask him how he did it, but he was a jackass, and couldn't stop talking about how fast his bike was because he had "modified the carbs" so i had to walk away. It looked pretty good, but off course it has the stupid lid instead of a nice filler cap.
it could have been just painted, House of colors has a 2 step chrome paint
when done right will look exactly like chrome.