Wow, the gasket wont fix that. If you can insert a piece of emt and make it work Id try it. The end where yours has rusted off is crimped from the factory to restrict flow for whatever reason, so I wouldnt worry about stuffing something inside choking it down abit.
Another option is at TBolt USA they have the trailbikes repop header and both heat shields for $20. I believe they have them mis priced, but I bought 3 of them to have around for that price.