My 71 was the same, I got the new bracket off Old Britts.
Cut what you can off, go close with a grinder if you feel confident (I am a boilermaker/welder) then finish with FILES.
Knock any weld down filing along the weld until you are close to the tube surface, then across with a rolling action.
Finish with a length of emery tape (1" wide) around the tube then the same in a 45 degree cross hatch X pattern.