Why are all these guys on Wulf's WTB thread?
David, you probably already know, but a center fill tank, metal, with the flange running vertically around the tank, was what was originally supplied. I have a nice plastic center fill I was going to use, but it sat very close to the front of the frame. I got a metal one as described from Johnny Tillotson and lined it with Caswells and painted it white.
At any rate, you don't need a corner fill tank with this bike, although it would make refueling slightly easier.