that's old school hot rod header wrap. The exhaust canister I bought, but I made the mounts, and flange out of plate steel, the 180 bend is a secret, but not hard to find if you think about it. Welded it up, and used to wrap to cover the ugly.
the tires are 26x2.5. There is no clearance issue, I just had to widen the rear triangle a bit, and add some nuts to the axle. I used billet aluminum BMX parts for the rear sprocket,. They are way lighter than stock. I've been rolling this ride for over two years. I rode it 11 miles every weekday for a year and a half. Ive made many 50+ mile rides as well. It's very dependable. 36 tooth gets me going 40+ MPH