Classic/Antique Car Repair: Car model, 63 impala, nascar circuit

Question
What is the   Difference  between. 1963 galaxy 500 and  63 and a half

Answer
The basic differences is the roof line.
Also known as the Fastback. In 1963 the Galaxy 500 was
introduced with the box-style roof and a 407 ci engine.

Chevy was beating Ford on the NASCAR circuit with the
63 Impala, so mid year Ford introduced the 63 1/2 FASTBACK
version with a slatted roof line for better aerodynamics and
later a 427 ci engine.

So, the 63 1/2 with a 427 engine was considered the Race Car.