Ha! 2M and I are on the same track.
I think you should repair and keep your original frame, it’s your number matching, and there is no stigma with repairing a break. I think it’s not so much a matter of abusing it in your youth, that caused the break. I believe it was just early in the learning curve for Japanese motorcycle manufacturing. Nowadays the frame would use thicker tubing , and computers to calculate stress points. I read an article about early frame development for the Norton Commando, they kept breaking up by the steering head. One of the engineers suggested a small triangular gusset and bingo! Problem solved.
As Jim stated, I think ideally, replace the entire tube. However if you choose to v out the crack and weld it, you will need to reinforce the entire area to prevent it from breaking again. I have repaired many broken truck and trailer frames in my youth as a fleet garage welder, and the formula was always the same, weld the crack, plate over it, reinforce it with gussets if it was near an intersection with an adjoining frame.
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