Jason,
You can stick any plug you want in there but if you plan on racing it the Champion/B&S plug is a spec item. Here is a link to Briggs racing web site along with a link to The Colorado Junior Karting Clubs web site. You can find all the info you need for the LO206. IMI Motorsports carries all the parts for this engine.
http://www.briggsandstratton.com/engines-racing/
http://www.cjkc.net/