Don't know about the welding part (Mark Twain said it was better to keep your mouth shut and appear to be a fool than to open it and remove all doubt) but on my first build, I sawed the muffler off and used a flexible copper water heater coupling to run the muffler back to the rear wheel. It did not seem to have a negative impact on performance. While it looked really cool, I later abandonded it because I could not get a good seal between the copper and the steel. I tried solder (it melted), JB weld and epoxy muffler patch (JB melts, the muffler patch was too brittle and broke every time) the result was oil on all of my shoes and pants. I'd say stick a piece on and give it a try.
