Thanks mate, appreciate that. I've used a welder only once before and the weld would probably be laughed at by all! Was fun doing it though.
I've contacted a couple of companies regarding Mongoose exhausts. Apparently they are still manufactured and I can buy just the section needed however there are long delays in manufacturing it, Larkspeed recommended I look for a custom replacement as they can't even say when the part would be available. I'm going to have more of a hunt around.