Anyone use a torsion my. crossmember Cap?

Myself I would say no. The best way to do it is cut all of the rust out and replace it. Anytime you sandwich the old rusted metal in there it just starts rusting the new parts. It's less work than replacing the whole crossmember but not what I would do if I was keeping the car. Now if you just want it to last a few years and flip the car then... well it's still up to you.