Could tig weld it but that part of the frame will need taking back to bare metal plus some surrounding paint could blister. Also you'd need to take the tank off, plastics etc and drain the carbs(safety first!). An easier idea might be just to clamp it on and araldite it with the blue tube stuff(the long cure stuff not rapid). Very strong once set and wont need much to hold it in place, maybe try first..
