The real question is, is it bent? or is it twisted from the torsion bar?
Mine was rusted and the torsion bar loads started twisting the crossmember, similarly to yours. I did cap mine, however that was only because I put a T56 6-speed and had to severely cut up that crossmember anyway.
I think yours is twisted. If it is, a cap will certainly help the situation, but ensure the torsion bar hex key is welded to it. So that load goes through the cap, not just under it. You will notice in my picture my "cap" is welded to the hex and is also plug welded to the original crossmember close to the hex. That whole area is 10ga plate and I just made the cap plates myself to tie to the subframe connectors. You'll also notice the forward member that I added to enforce that entire area as well. In other words, it's not going anywhere..