NickC wrote:What does "1503 XO/GCC" signify?
1503 Is the car number
XO Designates the motor. XO class consists of overhead valve (OHV) and flathead inline, V8 (except Ford and Mercury) and V12 engines, 1959 or earlier design, up to 325 cubic inch displacement.
And GCC designates it as a competition coupe or sedan, In this case sedan.