[BadNewsDan]

I would tack weld some flat stock to the tubes about 6 inches behind the neck to hold the shape of the frame, than cut the tubes an inch from the neck. Heat up the neck with a rosebud torch remove the tubes. Turn up some slugs on your lathe to fit the ID of the frame tubes press fit them into the tube and rosette weld them. Fit new peices of tubing to desired length and weld around the outside.