Keep them guessing. We built a 340 in the 80's in a 4 door 67 Dart. Used the 273 valve covers and air cleaner. Double gasketed the valve covers so the rockers wouldn't hit them. Used to go hunting Chebbies and Ferds. A lot of the hated that a 4 door 273 car smoked them light to light. Fun times. Even now my 422 looks just like a regular 340. Still have fun with it .