Glider
Captain
The rear tank didn't impact rear vision. As for the imbalance the Mustang had exactly the same problem and as long as you used that fuel first it wasn't a problem.Especially by ensuring that the pilot couldn't see what was behind him, also that the airframe was completely out of balance as long as there was fuel in the tank. The only way to keep the Spitfire V balanced, with a fuel tank behind the pilot, was to fit a 270-gallon ferry tank under the fuselage (check the manual.)
The very first Spitfires built were tail heavy and they simply put weights in the nose. As the aircraft gained weight the weights were moved to the back I don't see why that couldn't be done again.