http://www.creative-engineering.com/index.php?page=shop.product_details&flypage=flypage-ask.tpl&product_id=29&category_id=25&option=com_virtuemart&Itemid=26
Don't do it! , I had a narrowed beam on my last bus, it was the worst thing I ever bought driving the van was a nightmare, I felt like one of the Ant Hill Mob. Keep the standard track or you'll be very sorry.