Mt. Vernon AE Install Question

Question for all you experts out there. I am doing an install up and through the roof. The exhaust pipe, however in off center in the back of the stove. What do I use to get started out of the back of the stove so that the piping is centered when going up?
Otherwise, it will look silly if the piping goes up not centered with the back of the stove. Someone said Quad makes a part for this?

Yes there is a part for this, it is the rear to top adaptor and shield. It has a sealed clean-out trap built in and a heat shield. It screws to the back of the unit and supports the weight of the pipe system. It is right in the price book that every dealer should have, out the of the three adaptors it is the most expensive one for the AE.