OK, Stage one will be to just move the clamp to the underside of the top tube. I want to keep it as high as possible so that it will be easier to clean up the weld inside the seat tube. It will also then be possible to move the top tube down below it in stage two if needed. I had first thought of making a pattern of the hole required in the seat tube and cutting the hole. I would then remove all remnants of the original part of the seat tube from the clamp tube and weld it onto the new location. However, it may be better to not cut the hole in the seat tube, do the weld, and then use a round file, die grinder, etc. to cut out what ever part of the seat tube that protrudes into the clamp tube? In either case I would insert the aluminum seat post in just barely past the weld area to act as a heat sink and backing bar.