If it was any cylinder except the steel one you have, I would just say bite the bullet and replace it with a new aluminum cylinder. Unfortunately, the receptacle in the LS-3 ONLY accepts that particular size, and they are difficult to find. The aluminum equivalent is too large in diameter to fit in the mount socket, and modifying the 'glass is a difficult job that brings its own problems with getting approval for the change. Where are you located? I might be able to direct you to a hydrotest facility that won't make you jump through flaming hoops. (Never a good idea with an O2 cylinder :-)