Under tail exhaust build

Was just wondering if anyone has removed the rear fender and go measurements of the hole it leaves? I'm gonna bring home the exhaust tube legos from work and see if I can get the room to build an undertail and a license plate holder. I would like to use the mounting holes from the stock rear fender for the hanger. I have access to a plasma cut table, mandrel bender and solidwork so if these come out right I could make a few!