Howdy Lazy77 and all:
The correct OEM carb for a '63 fairlane with a 200 engine should be a C3OF-AA or AM. This code would be on a small metal tag (if you're real lucky) attached to one of the top cover screws. It will have an automatic choke. It only came with an automatic trans so a dash pot on the side opposite the accelerator pump should be present.
With a 43 year old car it is not uncommon to have a mix and match of parts. In 1963 engines came as 144, 170 and the brand new 200. The Autolite 1100 carb on a 144 came with a 130 cfm rating, the 170 with a 156 cfm rating and the 200 with a 185 cfm rating. Unfortunately these carbs look identical from the outside- except for the manual or auto choke, and the automatic trans dashpot. The only real difference is the inner diameter of the venturi and the main jet size.
The only way to determine the cfm of your carb is to measure the inner diameter of the venturi, or the narrowest throat inside the carb. So long as the engine is running good and you're satisfied, this is not worth doing. The time to do it is when the carb needs a rebuild and kit.
What Trans is in the car?
You can increase your mileage by-
*increasing the initial advance setting of the ignition, *airing up your tires to the max printed on the sidewalls of the tires,
*Set your low speed idle air screw to the highest manifold vacuum reading, and
*reducing your engine idle speed to the minimum.
HOpe this will help to get you where you want to go.
Adios, David