Go by the number on the trim tag, it's a 1964 car that someone put a 1963 front clip on. There wasn't any sort of 1963 1/2 car. Your VIN tag on the car's title (as well as on the driver's door pillar) should also decode to a 1964 car; you can look at the VIN decoding information at
http://www.1963pontiac.com/tools.htm or
https://www.tpocr.com/pontiacvin.html