Look at the subframe connector threads in the Cornering forum here. I doubt that 1x2 tubing would add that much torsional stiffness. The cowl crack is probably due to a hidden defect from the time the car was built or because of a collision long ago. I recall reading your posts, as I remember, you don't stress your car very much. The connectors may be a waste of effort and $$ if you drive conservatively.