Without a dust shield you will be replacing the front trans seal, as dust will collect around the damp area by the seal and eat it up. (as well as groove the hub)
The bar is a engine to trans support, and there isn't much you can do about that if the headers are in the way.
Just a slight increase in the possibility of cracking the bellhousing without it.
I would put the cover on for sure, and I was only able to get one support back in with headers.
