Is the water pump on a 1972 Chevy truck with big block short or long shaft?

The water pump shaft length on a 1972 Chevy truck with a big block depends on the specific engine and accessories used. There's no single answer. You'll need to consult a parts catalog or a reputable parts supplier using the engine's specific identification number (often found on a casting on the engine block) to determine the correct water pump. They can identify the correct shaft length based on that information.