The most elegant way to treat the exterior, if only moving the furnace 6", would be to fashion an aluminum plate that would both cover the original exhaust and intake holes and afford a mounting flange for the new exhaust and intake duct locations.
If you were close to me, I'd have this done for you in an hour, as I do some metal working with aluminum and have the needed plate on hand. A metal worker would view this project as fairly minimal.
Beyond the duct work, you might have wire stretching and copper propane piping to deal with, neither of which is terribly hard.
Good luck with the rearrangement.