I have two shift tubes. One has a good bottom but bad top. The other has a good top tab but bad bottom. Trying to make one out of two. I thought drilling out the two round spots would release it but it appears that the / / marks are welds also.
The process is the same as what
@Oldtimer described, except instead of drilling, you want to grind away the "tube" from the inside.
Just cut off the tab thru the tube with a cut off wheel. Once it is free, you can turn it over and grind off everything that isn't part of the "tab"
If you are worried that you won't be able to hold it while you are grinding on it, you can chop off the tube, and then split the tube and un-roll it. Then you can mount the unrolled tube in a vise while you grind it away.
Stop drilling holes in the tab, or there won't be any metal left to weld back.