If it's a jr sprint or kid sprint, then likely you'll be using a Briggs World Formula engine. I have not heard of any using the LO206 (yet) but that may be the case. Now, the winged outlaw karts run the LO206 in a lot of parts of the country.
Your rules dictate what pipe that you must run. I know the jr sprints have a spec pipe, as do the winged outlaw karts (5530 is the preferred wok pipe.)